SSE has paid out £190,000 in compensation to customers after it withdrew from a partnership with social enterprise Ebico, and failed to quickly move customers onto another tariff.
Suppliers have 49 days to move customers onto a new tariff if the one they are on is withdrawn, but SSE failed to comply with its licence by taking almost six months to switch customers over.
On Thursday, SSE said it had compensated all the customers affected and had a customer support team for those who needed further help.
Ofgem did not pursue formal action against SSE because the company had taken steps to help affected customers.
After it ended its deal with SSE, Ebico entered into a partnership with Robin Hood Energy, a not-for-profit company owned by Nottingham City Council.
Ebico contacted all the SSE customers on its tariff and said they would be switched onto a better rate with Robin Hood Energy automatically.
However, an automatic changeover would have contravened the supply licence, as customers needed to give their permission before being moved over to Robin Hood Energy.
Following discussions with Ofgem, the SSE customers were made aware of their option to switch, but were not automatically changed over to a new supplier.