Energy customers whose accounts were in credit when they closed them have been refunded almost £670 million over the past two years, according to Ofgem figures – which also show £97 million is still owed to in-credit customers. Contact your former supplier ASAP if you think you're among the many consumers owed money.

Data from the energy regulator published today shows that large suppliers have paid back almost 90% of closed-account balances outstanding since 2014, which is when the industry agreed to do more to reimburse customers who had closed accounts that were in credit.

However, many thousands of customers are still missing out on a refund, with Ofgem's figures showing £97 million – which equates to about 10% of closed-account balances built up since 2014 – is owed to customers.

It should be up to your former energy supplier to contact you about a credit refund and the 2014 agreement dictates that payments should be made within 14 days of a final bill being issued. But some suppliers are seemingly not keeping their side of the bargain and so you may have to chase them for your refund.

In the meantime, use our free Cheap Energy Club to see if you can save £100s by switching to a cheaper deal.

How can I claim a credit balance refund?

Before closing your energy account you should take a meter reading and make sure you're aware how much credit you've built up on your balance (if any). Check this info against what appears on your final bill.

If your former supplier plays by the book it should pay back any credit left on your account within 14 days of your final bill being sent. However, in some cases this doesn't happen.

If you're owed a refund but haven't heard from your ex-supplier within 14 days you should take matters into your own hands and chase it up.

If you're unhappy with its response or don't get one at all within eight weeks, you can go to the Ombudsman.

Why aren't some suppliers providing refunds?

Ofgem accepts that in some circumstances, it may be more difficult for suppliers to return long-standing credit balances, eg, if the former customer has moved and cannot be traced.

If suppliers are unable to find ex-customers after two years of trying, they will pay any outstanding credit into charitable funds. Yet despite this, Ofgem has confirmed that former customers can still claim for credit refunds two or more years after the account was closed.

Make sure you keep track of your credit balance

Today Ofgem also published new advice for consumers about account balances, for current and closed accounts.

For current customers, large suppliers typically review customers' accounts yearly and automatically pay back any outstanding balances. Even so, you should regularly check your bills, especially to see if you have a balance outstanding at the end of spring.

This is because balances for customers paying by direct debit are largely seasonal. People tend to build up credit balances during the summer when they use less energy.

Credit balances are drawn down during winter when people crank up the heating. Current customers are in credit on average by around £130 each in October before winter bites.