Gas and electricity supplier npower has written to its 3.4 million domestic customers and donated £1 million to vulnerable consumers after billing errors led to it being the most complained-about energy company.
Regulator Ofgem said there had been a "serious deterioration" in customer service levels after the German firm admitted a glitch had led to a number of errors.
The errors included; a number of bills and statements failing to go out on time, direct debit payments not being set up properly and some customer accounts having problems being started
npower chief executive Paul Massara said that anyone affected would not lose out financially as a result in his letter to customers.
Ofgem said it had been increasingly concerned about npower's customer complaint levels, which have risen sharply in the last year, but welcomed the apology and payment.
More top news
Headliners taking to the stage during the weekend will be Kasabian, Depeche Mode, Liam Gallagher and The Killers.
Official statistics show there were 82,694 inmates in jails in England and Wales on Friday.
Fears have been raised about the safety of the structure after the blaze last Friday night.