Consumers already pay over the odds for their energy bills and it’s unacceptable that some are still being let down by poor customer service,” she added. Data from the Citizens Advice Bureau shows that most complaints received about UK energy firms relate to two of the smaller , “ challenger ” brands – Extra Energy and Co - Operative Energy . The two firms received the highest number of complaints relative to their customer base size in the last three months of 2011 , in part because their rapid growth outpaced their customer base resources . The only big six firms to appear in the bottom ten of the league table , behind Extra Energy and Co - operative Energy , were Scottish Power and Shell , which have both faced billing issues caused by IT system upgrades . SSE , which laid claim to the lowest complaint rate in the industry since the table was first published five years ago , was narrowly beaten to the top spot by EDF Energy .
Data from the Citizens Advice Bureau shows that most complaints received about UK energy firms relate to two of the smaller , “ challenger ” brands – Extra Energy and Co - Operative Energy . The two firms received the highest number of complaints relative to their customer base size in the last three months of 2011 , in part because their rapid growth outpaced their customer base resources . The only big six firms to appear in the bottom ten of the league table , behind Extra Energy and Co - operative Energy , were Scottish Power and Shell , which have both faced billing issues caused by IT system upgrades . SSE , which laid claim to the lowest complaint rate in the industry since the table was first published five years ago , was narrowly beaten to the top spot by EDF Energy .