The regulator says that £40 million was added to customer bills from 2011 to 2019

Ofcom has today concluded an investigation into claims that O2 had overcharged its customers, today fining the operator £10.5 million.
The investigation found that O2 had inadvertently overcharged over 250,000 customers between 2011 and 2019, with many customers being billed twice in the same month.
The operator’s systems had attempted to overcharge customers by around £40.7 million across the eight year period. Despite around 140,000 customers paying these charges, the total O2 actually received totalled around £2.4 million.
O2 told Ofcom that it had been aware of the problem with its billing process since 2011, but had been unsuccessful in resolving them. O2 themselves notified Ofcom of the issue in July 2019.
“We identified the issue ourselves and notified our industry billing auditor. We have also taken proactive steps to refund all impacted customers for the extra charges they paid, plus an additional 4%,” said the company in a statement. For overcharged customers O2 was not able to reach, an equivalent monetary donation was made to charity. 
Ofcom said that O2 has refunded its affected customers and that the regulator was satisfied the company had taken sufficient action to prevent such errors occurring in future. The regulator was initially considering a £15 million fine, which was subsequently lowered once O2 accepted responsibility.
O2 is not the only operator in the spotlight for overcharging customers recently. BT is currently facing a class action lawsuit from disgruntled customers who are seeking £600 million in reimbursement for being overcharged for landline usage between 2009 and 2017. If successful, the case would see each of the claimants paid around £500 each.
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