The major energy supplier received 306.8 complaints per 100,000 customers for the final quarter of 2013, and up from 235.1 for the previous three months.
Citizens Advice stated there had been “no improvement” in the number of complaints made against Npower, with bills arriving late, payments being stopped, and new accounts not being set up.
When Npower’s chief executive Paul Massara joined the company in January 2013, he staked his reputation on getting Npower to the top of the customer satisfaction charts by 2015, and he stands by this pledge.
At the end of 2013, Massara wrote a letter to all of Npower’s customers to apologise for the poor levels of customer service.
Citizens Advice chief executive Gillian Guy said: “It is unacceptable that Npower has not yet sorted out the serious failings in its billing systems and customer service which are causing so many complaints and serious problems for its customers.”
Roger Hattam, Npower director of domestic retail, said the company was making “good progress in dealing with the root causes” of the problems, but remains “totally committed to resolving any problems”.
Scottish Power also suffered in the latest figures, falling from second place to 5th, with the number of customer complaints doubling to 100.5 per 100,000 customers.
Top of the table was SSE, with only 31.5 complaints per 100,000 customers.
Will Morris, group managing director, retail at SSE, said: “The figures show that there’s no such thing as the Big Six when it comes to customer service, with our worst competitor receiving ten times more complaints.”
British Gas (53.7) came second, ahead of Eon (55.8) and EDF Energy (62).