In April 2018, Ofgem ruled that energy suppliers couldn’t ‘back-bill’ their customers for energy that was used more than a year ago.
Back-billing is when suppliers estimate bills due to not having regular, accurate meter readings. Once they have the meter readings, the supplier might send a catch-up bill if the estimated amount was too low. The only exception to this ban is if a customer prevents an energy company from taking accurate meter readings, for example by refusing access to the meter to take a reading.
If this happens to you, and you don’t believe you owe this money, you do have the right to lodge a complaint with the company. If you don’t receive a satisfactory response, you can escalate your complaint to The Energy Ombudsman.
You must not ignore any letters that you receive about your energy bills, whether it’s from your current supplier or a previous one. Even if you disagree with the amount that you’ve been billed, there’s still a possibility that you owe some money.
If the company that sent the letter doesn't hear from you, they may consider pursuing enforcement action through the courts if you live in England and Wales or through the courts if you live in Scotland, which could further complicate the problem.