The UK's media regulator has criticised O2 for raising its prices by more than it promised customers when they took out their phone contracts.
Ofcom said it was "disappointed" with the firm, and said it was going against "the spirit of our rules" around being transparent to customers about price rises.
In January, new rules were brought in to stop phone and broadband companies raising prices in the middle of a contract without warning.
O2 said it has not gone against the regulation and that Ofcom's rules "do not prevent companies from increasing annual price changes – for example, to invest in improving networks".