EDF Energy has acknowledged that its customers were caused significant disruption when the firm introduced a new IT system in 2011 and has publicly apologised for this.
Ofgem said that the firm's payment of £3 million to vulnerable customers was a "step in the right direction".
EDF Energy failed to have sufficiently robust processes in place when they introduced a new IT system and this led to the unacceptable handling of complaints.
Their commitment to putting things right and paying £3 million to the Citizens Advice Energy Best Deal Extra scheme and the Plymouth Citizen Advice Bureau's Debt Helpline to benefit vulnerable customers is a step in the right direction to rebuilding consumer trust.
More top news
A legendary Bunny, leisure centres and protests from the Anti-Nazi League. There's plenty to learn as Murray and Co bid for tennis glory.
Natasha Kaplinsky has interviewed survivors and liberators of Nazi concentration camps to hear untold stories of the Holocaust
The man jumped the fence while the president and his family were inside celebrating Thanksgiving but was quickly apprehended.