E.ON has axed at least 20 call centre staff for rudeness and cutting off customers who had rung in, it was reported over the weekend.
The supplier sacked around 20 employees from its Bolton head office and there may have been more dismissals in other offices, the Mirror reported. It was part of an internal review of customer service.
Customers were allegedly left on hold for too long or not dealt with politely enough while other people were just cut off.
The supplier has found itself in hot water with regulator Ofgem more than once in the past few years. Last year Ofgem launched an investigation into its sales techniques while in 2011 it was asked to pay back £1.4million to around 94,000 customers it had overcharged or charged exit fees.