Complaints about the "big six" energy firms soared by 26% over the summer as hostility against the sector continued to mount, a watchdog said today.
Just one firm - ScottishPower - saw complaints drop on the previous quarter, while EDF Energy was rooted to the bottom of Consumer Focus's league table after a near-75% leap in customer grievances between July and September.
The London-based firm, which became the first supplier to have a zero star rating, issued an apology to customers after admitting the introduction of new billing systems had affected its performance.
The industry-wide surge in complaints follows a period when all the major firms announced bill hikes for the winter and as the regulator Ofgem stepped up its pressure on firms to address issues such as overly complex tariffs.
Consumer Focus director Adam Scorer said: "It is disappointing, but perhaps not surprising, that complaints on energy issues have risen at a time whenenergy bills are increasing.
"Energy companies have repeatedly said they want to rebuild consumer trust. Good customer service and complaints handling are key ingredients to building consumer trust but suppliers still have a long way to go."
The data is based on complaints that have been weighted to reflect their seriousness and the time and effort spent by the consumer to get their problem resolved.
EDF's new systems caused billing issues for customers, some of whom were unable to get through on the phone when they had a problem.
The problems came even though the company took on 700 additional customer service staff to cope with the transition period.
It said: "As soon as delays occurred we recruited an additional 400 service staff, which naturally took time to become effective, and we slowed down our plan to move customers on to the new system to ensure service levels were stabilised and restored.
"The actions taken and investments made are paying off and the service to our customers is improving."
The other two companies that dropped a star on the ratings table were npower (from three to two) and E.ON (four to three).
SSE - formerly known as Scottish & Southern Energy - retained its five star rating at the top, British Gas was ranked in second place with four stars and there was no change with Scottish Power on three stars.
Meanwhile, Consumer Focus said it was "concerned" about Scottish Power and EDF's failure to include the watchdog's contact details in letters notifying customers about price hikes.
It said this may have had an impact on the level of complaints for the various suppliers.
Price increases varied across the industry, with Scottish Power increasing the price of gas by the highest margin with a 19% hike, while electricity was pushed up the most by British Gas with a 16% increase.
EDF's rises of 15.4% for gas and 4.5% for electricity were the smallest increases overall.