The mobile operator O2 has been fined £10.5m for overcharging 140,000 customers several million pounds as a result of billing errors that persisted for almost a decade. The telecoms regulator, Ofcom, said the fine – which was reduced from £15m because of O2’s cooperation with its investigation – related to errors in the final bills received by customers leaving the operator. The investigation found that between 2011 and 2019 an error in the way O2’s systems calculated final bills meant that many customers were billed for some fees and charges twice. More than 250,000 customers were billed a total of £40.7m in incorrect charges. The bills of many of the customers being disconnected were already in arrears, meaning they did not actually pay the incorrect extra charges, but 140,000 departing customers did pay £2.4m in fees they should not have. “Mobile customers trust their provider to bill them correctly and fix errors as quickly as possible,” said Ofcom’s enforcement director, Gaucho Rasmussen. “But these billing issues continued for a number of years without sufficient action from O2, and thousands of customers were overcharged as a result. “This is a serious breach of our rules and this fine is a reminder that we will step in if we see companies failing to protect their customers.” Ofcom said the UK’s biggest mobile operator had initially identified the problem with its billing processes as far back as 2011 but “efforts to address these problems were not successful and customers continued to be overcharged”. O2, which has fixed its billing process, has refunded all the customers affected in full, plus an additional 4%. For those the company has been unable to track down, a donation equivalent to the overcharged amount has been made to charity. “We are disappointed by this technical error and sincerely apologise to customers impacted,” an O2 spokesman said. “As Ofcom have stated today, the vast majority of funds reported were not overpaid. We identified the issue ourselves and notified our industry billing auditor.”