It was Co-op that had the most number of complaints per 100,000 customers between July and September, according to the Energy Ombudsman.
There were 13,212 energy complaints received during this period, taking the total figure of complaints received to more than 50,000 enquiries received so far in 2015.
Of these billing issues, such as disputed charges, inaccurate invoices and missing bills, irritated Britons most, accounting for nearly nine out of every ten complaints. And this was followed by transfers, which relates to issues with switching from one provider to another or from one tariff to another.
Chief Ombudsman Lewis Shand Smith said: "Consumers are rightly more demanding of their energy suppliers than ever before, taking service as well as cost into account.
"Having easy access to these figures gives consumers the power to make informed decisions about their energy provision. It’s clear that energy companies’ steps to improve their customer service are starting to pay off, but there is still more that could be done to ensure the service customers receive matches their expectations."
The ranking includes the big six energy companies - British Gas, EDF Energy, E.ON, npower, Scottish Power and SSE - as well as some of the smaller "challenger" suppliers such as Ovo Energy and First Utility.