As many as 2.1 million households could have been hit by large late bills in the last year because energy suppliers initially undercharged them, Citizens Advice reveals.
According to the charity, the average back-bill received was for £206, while 15% of those who had been back-billed said they were charged more than £250.
But people contacting the Citizens Advice service have reported much larger back-bills. One person who asked the charity for help was billed out of the blue for £1,120 - the supplier had only sent them estimated bills, had never read the meter over a five-year period, and later demanded full repayment.
The charity also helped a blind man who set up a monthly direct debit because he could not take meter readings – who three years later received a back-bill demanding £3,500 after the supplier said the monthly payment had been an underestimate.
Are energy providers allowed to back-bill customers?
Back-billing can occur when providers simply don’t send you a bill, or when they have realised they’ve made a mistake with how your bills are calculated and you’ve therefore been underpaying.
But energy suppliers can’t back-bill customers for energy used more than 12 months ago, if the company itself is at fault for not having sent the bill in the first instance.
Be aware that this is unlikely to apply if you’ve been using the gas or electricity supply but have made no attempt to contact the supplier to arrange payment.
My supplier isn’t following the rules. What can I do?
Billing errors are the number one energy problem people contact Citizens Advice’s consumer service about, with 16,000 cases last year.
But if you believe your supplier is wrongly back-billing you, you first need to complain to it. You can use the free Resolver tool to help.
If this doesn’t work, or you don’t get a response, you can take your gripe to the free Ombudsman Services to look into.
‘Customers shouldn’t have to pay for suppliers' mistakes’
Gillian Guy, chief executive of Citizens Advice, says: “Customers shouldn’t have to pay the price for suppliers’ mistakes.
“Energy bills are already high so it adds insult to injury when companies go back to customers looking for more money after they got it wrong.
Particularly for suppliers who insist on payment in full, this can be a huge burden on already stretched finances.”