Disgruntled consumers were turning their backs on the Big Six in favour of smaller independent energy suppliers, according to the Energy Advice Line.
Julian Morgan, managing director of the price comparison, switching and advice service, said increasing numbers of domestic and business energy users were voting with their feet to get a better deal.
"High prices, poor service and tarnished reputations of the big energy suppliers are prompting more and more consumers to consider their options," Mr Morgan said.
"Lots of consumers are now switching to small, independent suppliers that might not be household names but are offering competitive deals and the prospect of better customer service.
"Smaller companies are often more nimble and customer-focused because they have to be competitive to get ahead.
"This is winning over customers who have lost faith in the Big Six. The big guys are now paying the price for not placing the interests of consumers at the centre of their business strategies."
Big Six supplier Npower recently reported a 38% drop in profit for the first half of the year, part of which was attributed to increased spending to improve customer service.
The supplier said it was on course to meet targets set by Ofgem to send out more bills on time, reducing the number of late invoices from 414,000 in mid-June to 193,000 by the end of July. The regulator has ordered that by the end of August no more than 100,000 bills should be sent late.
EDF has also been forced to tackle poor customer service following an Ofgem investigation into how the company handled complaints.
The regulator found a new IT system introduced by EDF did not have the means to properly receive, record and process customers' grievances. It ordered the company to pay £3 million "to benefit vulnerable customers" as a result of the inquiry.
"These recent developments are just the latest examples of why consumers are seeking refuge with newer and smaller suppliers that are keen to win new business," Mr Morgan said.
"Although competition in the energy market is still not working properly, this does not mean that all suppliers are the same because they're not.
"We have a number of highly-competitive independent firms on our panel of suppliers, and consumers would do well to consider switching over to them.
"We would be pleased to help consumers compare the prices of the established Big Six and the smaller firms. Many of our customers have been pleasantly surprised at the amount they can save."
The Energy Advice Line is one of the UK's leading price comparison and switching services for business and domestic energy customers. It is also an advocate for energy market reform and has campaigned for a better deal for energy users, including calling for a ban on cold calling and changes to regulations to make it easier for all consumers to switch suppliers.
The service is completely independent and free. Consumers can quickly and simply search the market for the best available energy deals from an extensive panel of small and large energy suppliers. The service also offers a free advice line for business energy customers.