Complaints about energy companies have risen to their highest level, according to data from the Energy Ombudsman.
In the first six months of the year complaints more than doubled to 22,671 - from 10,598 for the same period in 2013 - with 84% related to billing.
The government said it was unacceptable that so many people were unhappy.
Energy UK, the industry lobby group, said the sector "works hard" and is investing in "resources and new systems" to resolve customers' issues.
Complaints made to the ombudsman about energy firms also reached a record for a single month, with 4,124 made in June, more than treble last year.
"The spike in complaints is in part a result of the rising cost of living, but also as a result of consumers becoming more aware of their rights and feeling more empowered to act and fight for a fair deal," said chief energy ombudsman Lewis Shand Smith.
A spokesman for Energy UK said: "The energy industry works hard to provide the best service for its customers but in an industry serving 27 million households sometimes things go wrong."
"However, no one wants to see complaints rise and each complaint is taken very seriously with companies working hard and investing in resources and new systems to resolve issues as quickly as possible. Most complaints are dealt with by the end of the next working day with no more than a phone call," said Energy UK.
A Department of Energy and Climate Change spokesman said: "Energy companies need to realise that people will not tolerate poor service and are switching suppliers in unprecedented numbers, particularly to small suppliers whose numbers have nearly trebled since 2010."
However, in a separate report, research from Ofgem shows three quarters of people in rented homes say they have never changed energy supplier.
One in five people did not think they were allowed to switch, said energy regulator Ofgem.
About nine million people live in private rented accommodation.
They were half as likely to switch their suppler compared with families who owned their homes, said the report.
"Research has shown that this group is not shopping around for their energy, and missing out on savings of up to £200," said Ofgem chief executive Dermot Nolan.
The report says 77% of respondents who rent have not changed their electricity suppler, while 74% have never switched their gas company.
Ofgem referred the UK energy industry to the Competition and Markets Authority (CMA) in June.
One of Ofgem's central concerns is the structure of the market which allows big companies to be both energy generators and suppliers to households. It wants the CMA's investigation to examine how this works and whether the relationship should be broken up.
Last month Ofgem also reached an agreement with the energy companies to make it easier for customers to switch supplier. Under the agreement customers will be able to switch energy supplier within three days by the end of the year.
Anyone who wants to switch must be given a two-week cooling-off period for the chance to change their mind, before the three-day process starts.
Next-day switching should be in place by the end of 2018 at the latest.
At present, the switching process can take five weeks, including the two-week cancellation period.
"A common myth among renters is that they have to accept the energy suppliers already in place when they move in. But very rarely is this the case," said Ofgem.