The Energy Ombudsman received 4124 complaints in June - representing the highest ever figures on record.
The watchdog's staff dealt with, on average, 196 issues each working day of last month, with the vast majority of complaints focusing on bills and related errors.
June's tally, which is more than three times that for June 2013, signals further consumer dissatisfaction with the energy companies in the UK.
Complaints have steadily increased over the last 18 months.
Complaints to the ombudsman during the first six months of this year have already surpassed the total received for the whole of 2013.
Lewis Shand Smith, chief energy ombudsman, believes the rising understanding of consumer rights has been one of the main reasons behind the increases.
He said: "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. Addressing these concerns is crucial to restoring consumer confidence."
Fraser Sutherland, spokesperson with Citizens Advice Scotland (CAS), added: "It has to be a concern that so many people are dissatisfied with their energy supplier. It's clear that energy companies have a lot more to do to provide customers with the level of service they are entitled to expect.
"However the growth in the number of complaints also reflects a more confident consumer, and that is to be welcomed.
"We encourage all consumers to speak up about their complaints, and to assert their rights as customers."
Energy tariffs continue to be the biggest source of contention with around 84 per cent of this year's complaints focused on billing-related issues. The second largest cause relates to transfer issues, accounting for around 13 per cent of all complaints.
These figures come as the energy industry approved a policy to ensure an energy company takes a minimum of three working days to facilitate the transfer of a consumer's supplier.
A spokeswoman for the Department of Energy and Climate Change said: "It is unacceptable that so many people have needed to complain about their energy suppliers.
"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."
The overall spike in complaints comes as Ofgem formally opened an investigation into Npower, after a series of ongoing complaints.
The supplier will be scrutinised over "prolonged customer service failings", the first under its new Standards of Conduct which state that suppliers must treat consumers fairly. ScottishPower has also been under intense pressure after CAS recently revealed complaints against the energy firm had more than doubled in the first quarter of this year.
Npower and ScottishPower introduced new billing systems in recent months, which has since caused major problems.
Both firms apologised last week over the increase in complaints and said they were committed to improving their customer service.
l More than three-quarters of bill-payers living in rented accommodation have never switched energy supplier, a poll has found.
One in five tenants said they were not aware it was possible to switch to another energy company, according to the latest data from Ofgem's 2014 Consumer Engagement Survey.