How to Write a Letter to an Energy Company About a Billing Error UK

Energy billing errors are more common than most people realise. From estimated bills that bear no relation to actual usage, to back-billing for years of undercharging, to charges above the Ofgem price cap, mistakes in energy billing can cost households significant amounts and cause serious financial stress. The good news is that energy companies are regulated, time-limited in what they can recover, and required to follow a formal complaints process that leads to the Energy Ombudsman if they do not resolve your complaint fairly.

This guide explains the most common types of energy billing error, what your rights are in each situation, how to write a complaint letter that gets taken seriously, and how to escalate if the energy company does not put things right.

Common Types of Energy Billing Error

• Overcharging against the price cap: Energy suppliers cannot charge domestic customers above the Ofgem price cap. In 2025, Ofgem secured £7 million in refunds from ten suppliers who had overcharged more than 34,000 customers by incorrectly applying standing charges above the permitted level. If you think your charges are above the capped rate, compare your unit rates and standing charges against the current Ofgem price cap figures.

• Estimated bills that are wrong: If your supplier has been issuing estimated bills based on inaccurate consumption data, you may have been over or undercharged. Submitting regular meter readings is the best prevention, but if you have been overcharged based on estimates, you are entitled to a corrected bill and a refund of any overpayment.

• Back-billing beyond the 12-month limit: Ofgem rules prohibit energy suppliers from charging for energy used more than 12 months before the bill is issued, where the reason for the delay was not the customer’s fault. If your supplier is attempting to recover a debt for energy consumed more than a year ago that it failed to bill for at the time, you can challenge this under the back-billing rules.

• Incorrect direct debit amounts: If your direct debit has been set significantly higher than your actual consumption warrants, you are building up a credit balance on your account that belongs to you. Suppliers must review direct debits at least annually and must refund credit balances promptly on request.

• Double charging or duplicate transactions: Payments charged twice, or the same charge appearing on consecutive bills, are errors the supplier must correct and refund.

• Charges after switching: If you have switched supplier and your previous supplier is continuing to issue bills or charge direct debits, write to them formally demanding they stop and refund any amounts taken after the switch date.

• Wrong tariff applied: If you have been placed on a tariff you did not agree to, or moved to a more expensive tariff without proper notice, this is an error you can challenge.

Your Rights: The Ofgem Back-Billing Rules

The back-billing protection is one of the most important rights energy consumers have and one of the least known. Under Ofgem licence conditions, energy suppliers cannot charge domestic customers for gas or electricity used more than 12 months before the bill is issued if the reason for the delayed billing was the supplier’s failure rather than the customer’s. As Ofgem’s back-billing guidance confirms, if you receive a large unexpected bill for consumption from over a year ago, check whether the back-billing rules apply. If they do, you can write to your supplier citing the back-billing limit and ask them to write off the debt for the period covered by the protection.

The protection applies where you have not had an accurate bill, have not been informed of charges due via a statement of account, or your direct debit was set too low to cover actual usage. It does not apply if you deliberately prevented meter readings from being taken or if there is evidence of energy theft.

Your Rights: Refund of Credit Balances

If your energy account is in credit, that money belongs to you. Suppliers must offer to refund your credit balance promptly when asked. If you are switching supplier, your old supplier must send you a final bill and refund any credit balance within six weeks of your switch. If they fail to do so, you may be entitled to automatic compensation under Ofgem’s Guaranteed Standards of Performance. The compensation is £30 for a final bill not issued within six weeks, with a further £30 if that compensation is not paid within ten working days.

Before You Write: What to Check and Gather

• Your most recent energy bills, including the billing period, tariff name, unit rates and standing charges

• Your meter readings for the period in dispute

• Your direct debit history, showing amounts taken and when

• Any correspondence from the supplier about the billing in question

• The current Ofgem price cap figures for your region and payment method

• Evidence of meter readings you have submitted, whether by app, online, phone or letter

• Any records showing when you switched supplier if relevant

Tip: If you have a smart meter, your supplier should have accurate consumption data and cannot rely on estimates. If your smart meter has not been communicating correctly, this may itself be a failing by the supplier that contributed to the billing error.

How to Structure Your Complaint Letter

State It Is a Formal Complaint

Use those words in both the subject line and the opening sentence. This triggers the supplier’s regulated complaints process and starts the eight-week clock they must respond within.

Identify the Error Specifically

Describe the billing error clearly. State the billing period involved, the amount charged, what you believe the correct charge should be and why. Reference your meter readings, the applicable price cap rates or the back-billing rules where relevant. Attach copies of the bills in dispute.

State the Amount You Are Seeking

Calculate the refund you are owed and state it clearly. If the error has resulted in multiple overcharges over several billing periods, list each one. If you are seeking write-off of back-billed debt under the 12-month rule, state the amount that falls outside the permitted period.

Reference Your Rights

Reference the relevant Ofgem rules where applicable. For back-billing, reference the 12-month back-billing limit under the energy supplier licence conditions. For overcharging above the price cap, reference the Ofgem price cap. For credit balance refunds, reference the Guaranteed Standards of Performance if the six-week deadline has been missed.

Full Worked Example

[Your full name]

[Your address]

[Your account number]

[Date]

Customer Relations / Complaints Team

[Energy supplier name]

[Address or email]

Subject: Formal Complaint – Billing Error – Account [number]

Dear Sir or Madam,

I am writing to make a formal complaint about a billing error on my energy account, account number [number], at [property address].

The error

[Describe the specific billing error. For example:]

[Overestimated billing: I have received bills for the period [dates] that are based on estimated readings of [X] units. My actual meter reading on [date] was [X], which is significantly lower than the estimate used to calculate my bill of £[amount]. I submitted a meter reading on [date] via [method] but this was not reflected in the bill issued on [date]. Based on my actual reading, I calculate that I have been overcharged by approximately £[amount].]

[Back-billing: I have received a bill dated [date] requesting payment of £[amount] for energy consumption during the period [dates]. The consumption forming the majority of this bill relates to the period [dates], which falls more than 12 months before the date of this bill. Under Ofgem’s back-billing rules, energy suppliers cannot charge domestic customers for energy consumed more than 12 months before a bill is issued where the supplier was responsible for the delay in billing. I did not prevent meter readings from being taken at any point. I am writing to ask [supplier] to write off the portion of this bill relating to consumption prior to [date 12 months ago].]

[Credit balance refund: My account currently shows a credit balance of £[amount]. I have been asking for this to be refunded since [date]. As of today, [X] weeks have passed without a refund being issued. I am formally requesting an immediate refund of my credit balance to my bank account.]

What I am requesting

I am requesting [a corrected bill reflecting my actual consumption / a refund of £[amount] representing the overcharge / the write-off of the back-billed amount of £[amount] dating to before [date] / an immediate refund of my credit balance of £[amount]]. I would also welcome a written explanation of how the error occurred and confirmation that my account has been corrected going forward.

I expect a response within eight weeks in accordance with your obligations under Ofgem’s Complaint Handling Standards. If this matter is not resolved to my satisfaction, I will refer my complaint to the Energy Ombudsman.

Yours sincerely,

[Your name]

[Contact details]

[Attachments: copies of disputed bills, meter reading records]

What the Energy Company Must Do

Under Ofgem’s Complaint Handling Standards, energy suppliers must acknowledge your complaint promptly and provide a final response within eight weeks. If they do not respond within eight weeks, or if their response is unsatisfactory, you can take your complaint to the Energy Ombudsman. You can also escalate immediately if the supplier issues a ‘deadlock letter’ confirming they cannot resolve the complaint to your satisfaction.

While your complaint is being investigated, the supplier should not take enforcement action to recover a disputed debt. If they are threatening to disconnect your supply or use a debt collection agency while a formal complaint about the billing is outstanding, write to them noting that the debt is disputed and that you have an active formal complaint.

Escalating to the Energy Ombudsman

If the supplier does not resolve your complaint within eight weeks, or issues a final response that you are not satisfied with, you can take your complaint to the Energy Ombudsman. The service is free to consumers. The Ombudsman can direct the supplier to correct the bill, issue a refund and make a goodwill payment for the distress and inconvenience caused. If the Ombudsman upholds your complaint, their decision is binding on the supplier. You have 12 months from the supplier’s final response to refer the complaint to the Ombudsman.

Getting Help

Free advice on energy billing disputes is available from Citizens Advice, whose energy advisers can help you understand your rights, check whether the back-billing rules apply and draft a complaint letter. Citizens Advice also has an Extra Help Unit for consumers who need support with complex or urgent energy complaints. If you want help drafting a billing error complaint letter that references the correct Ofgem rules and gives the supplier what it needs to act, the team at LetterLab can help you get it right before you send it.

Quick Checklist: Before You Send Your Complaint

1. Does the subject line use the words ‘formal complaint’?

2. Have you identified the specific billing period and error with precise amounts?

3. Have you attached copies of the disputed bills and your meter reading evidence?

4. Have you calculated and stated the exact refund or write-off you are seeking?

5. Have you referenced the applicable Ofgem rules: back-billing limit, price cap, Guaranteed Standards?

6. Have you noted the eight-week response deadline and mentioned the Energy Ombudsman?

7. Are you keeping a copy of the letter with a note of the date you sent it?

8. If the debt is disputed, have you noted in the letter that you do not accept it is owed while the complaint is outstanding?

The Key Takeaway: Energy Billing Errors Are Winnable Complaints

Energy billing errors are regulated territory. Ofgem sets the rules suppliers must follow on billing accuracy, back-billing limits and credit balance refunds. When suppliers get it wrong, there is a clear complaints process, a free independent Ombudsman and real enforcement behind it.

Write formally, identify the error precisely, state what you want and reference the rules that have been broken. If the supplier does not respond properly within eight weeks, the Energy Ombudsman can put it right at no cost to you. These are complaints worth making.

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