Communications regulator Ofcom is urging mobile phone customers to reclaim money owed to them when they switch contracts.
According to its figures, mobile phone companies have trousered some £10 million left languishing in defunct accounts over the past two years. Some two million people have each left an average of a fiver in their old accounts.
The regulator is putting pressure on mibile phone companies as well as broadband and landline suppiers to refund punters automatically.
Until recently only BT, Orange and the Post Office automatically refunded all outstanding credit on their customers' accounts. But T-Mobile has now agreed to do so and Vodafone said it will do the same but for its direct debit customers only.
O2 will only automatically credit sums of more than £20, while Virgin Media agrred to do automatic refunds from December.
That leaves Sky, Talk Talk and Three who are dragging their heels. They refuse to refund customers unless they are contacted first. They find it hard to hand over money that isn't theirs to people who don't ask for it
"Consumers were telling us that they found it difficult to claim unused credit from their providers when they left their contracts," Ofcom chief executive, Ed Richards said.
"Taken together, people have been millions of pounds out of pocket as a result.
"We hope that automated refund processes, clearer signposting by providers and our new consumer guide should help consumers claim back money that is rightfully theirs," he added.