Energy watchdog Ofgem has demanded that suppliers improve their poor complaints handling.
Ofgem has written to the Big Six as well as smaller suppliers about the "industry-wide failure" to handle complaints to an acceptable standard.
Its research found that more than half of those who had complained were not satisfied with the way it was handled by their energy supplier.
Meanwhile in nearly half of cases where the supplier considered the case resolved, the customer did not.
Satisfaction with Npower and Scottish Power has fallen particularly markedly, Ofgem said, with only SSE managing to maintain levels of satisfaction found two years ago.
Dermot Nolan, Ofgem chief executive said: “Satisfaction scores are frankly awful. Almost all energy suppliers need to improve their complaints handling as a matter of urgency.
"There are real business benefits to good complaints handling schemes, and it shouldn’t need a regulator to tell companies about the importance of this.
“Suppliers must now tell their customers what steps they will be taking to put things right. We are already formally investigating Npower about complaints handling and other customer service issues, and this should send a strong signal to all suppliers that, where necessary, we will take action."
“It shouldn't need involvement from Ofgem for energy companies to get the basics right,” said Richard Lloyd of Which?
“Energy companies have hit rock bottom with woeful service and dreadful complaints handling and the situation has been going on for far too long. It’s little wonder that consumer trust is so low.”
