T-Mobile apologise for overcharging customers
UK mobile firm T-Mobile has apologised for an error that saw thousands of customers charged for calls they did not make.
It is believed that the problem has affected 4% of T-Mobile's customers, all of whom will be fully refunded.
The firm blamed the issue on a "glitch in our billing systems".
In unrelated news, Ofcom has promised to investigate the problem of unexpectedly high bills.
The issue was first brought to light by consumer website Bitter Wallet, which estimated that up to half a million customers could have been affected.
T-Mobile said the problem was down to a technical error.
"Some T-Mobile customers wrongly received call forwarding charges when they used their voicemail," the firm said in a statement.
"This problem has now been fixed. We'll be fully refunding every customer affected by this, a process which has already begun. We're really sorry and wholeheartedly apologise to any customers who have been affected by this issue," it added.
High bills that are legitimate but unexpected are also becoming a big issue for consumers and Ofcom is considering whether the problem needs further regulation.
People who have used their phones abroad are particularly likely to be lumbered with huge bills but other reasons include users going over their monthly allowance, using premium rate numbers or downloading large amounts of data.
According to Ofcom, 6% of UK consumers received an unexpectedly high mobile phone bill over the last 12 months. Of those, 18% received a bill of over £100 more than expected.
Ofcom wants to hear from consumers who have received such bills.