EDF Energy tops the list of the most complained about energy suppliers, new figures published by Consumer Focus show.
The lobby group's quarterly energy complaint league table shows, of the so-called 'big six' suppliers, EDF was the only provider to see an increase in complaints in the first three months of 2012.
The company has now received the most complaints for the fourth quarter in a row.
However, there was a 7% average drop in the number of complaints against the six biggest energy firms — British Gas, Eon, EDF, Npower, Scottish and Southern Energy (SSE), and Scottish Power.
Between January and March this year EDF received 195.3 complaints per 100,000 customers, up from 188.5 in the last three months of 2011. The figure is almost double that of Npower, which had the second highest number of complaints with 89 per 100,000.
The firms are ranked on the number of complaints to Consumer Direct, Consumer Focus and the Energy Ombudsman
SSE registered the lowest amount of complaints, with just 35.4 per 100,000 customers from January to March. It is also the only company to be awarded the Consumer Focus five star top rating.
Scottish Power gains a four star rating after a 21% fall in the number of complaints from the previous quarter. British Gas retains a four star rating whilst Eon and Npower both stay on three stars.
Audrey Gallacher, director of energy at Consumer Focus says: "Suppliers have said they want to increase consumer trust in the industry so they need to build on this result and work towards achieving consistently good customer service.
"It is however disappointing to see yet another poor performance from EDF Energy. The firm has made some big commitments to improve its performance and its customers will rightly expect to see it getting back on track on customer service."
An EDF spokeswoman says: "We are obviously disappointed that our service levels are not at the high standards we expect and our customers deserve.
"We recognise that we must improve and are absolutely determined to get better."
How to complain
If you have a complaint or are experiencing difficulties, the first thing you should do is contact your energy supplier.
The big six energy firms have an obligation to resolve your problem in no more than eight weeks. If it's not resolved in that time or you are rejected, contact the Energy Ombudsman, which is a free and independent service that investigates complaints.
Firms are ranked on the number of complaints to Consumer Direct, Consumer Focus and the Energy Ombudsman.