The public furore over the cost of living and rising energy bills has prompted an increasing number of people to shop around for cheaper deals.
Big six supplier Npower still had the most dissatisfied customers, but independent supplier Good Energy saw the biggest increase, with complaints rising 466 per cent over the past six months.
Complaints to smaller firm Utility Warehouse rose 52 per cent over the same period, according to Ecotricity.
“While the massive upheavals in the industry appear to be having a knock-on effect for customer service standards across the industry, some independents appeared to be struggling to adapt to the extra demands of customer growth,” said the research.
Overall energy industry complaints have risen by 23 per cent in the past six months.
The number of customers switching energy suppliers grew for the third month in a row in April, hitting a total of 289,000, according to figures from Energy UK earlier this month.
The number of people switching to smaller suppliers reached an all-time high of 135,000, equating to a record 46.88 per cent of all switches.
It currently takes around five weeks to switch suppliers. Energy secretary Ed Davey wants this to be reduced to one day.