The mobile phone company Giffgaff has been fined £1.4 million by Ofcom for “unacceptable” billing errors, after it overcharged around 2.6 million customers.
The industry watchdog said that the company, owned by O2 network operator Telefónica, overcharged customers by a total of nearly £2.9 million between May 2011 and February 2019.
It found that Giffgaff had been overcharging customers who bought its pre-pay bundles of voice minutes, text messages and data - called "goodybags" - between May 2011 and February this year.
Ofcom's director of investigations and enforcement, Gaucho Rasmussen, said getting bills right was a "basic duty" for phone companies.
He said: "Giffgaff made unacceptable mistakes, leaving millions of customers out of pocket."
Giffgaff has already refunded around £2.1 million to affected customers, but in cases where it was unable to trace customers, it has donated their refund money to charity.
Ofcom reduced the fine - which will be paid to the Treasury - by 30 per cent after the network provider agreed to settle and reported the mistakes to the regulator.
But Giffgaff was hit with an extra £50,000 penalty for failing to provide accurate information to two of Ofcom’s requests during its investigation.
Mr Rasmussen concluded: “This fine should serve as a warning to all communications providers: if they get bills wrong, we’ll step in to protect customers.”