Energy firm Npower apologises for billing errors
Npower is writing to its 3.4 million domestic customers to apologise for problems with its billing process.
In November, figures from the official consumer watchdog found that Npower was receiving five times more complaints than the best performing energy firm.
Npower has vowed to tackle problems over setting up accounts, direct debit payments and billing.
In addition, it is donating £1m to a scheme assisting vulnerable customers.
The company, which increased the average domestic dual-fuel bill by 10.4% at the start of December, recorded 202 complaints per 100,000 customers in April to June, according to recent figures from Consumer Futures.
Its complaints levels were the highest among the big six, followed by EDF (75 complaints per 100,000 customers), then E.On (60 complaints per 100,000 customers), British Gas (55), Scottish Power (41), and then SSE (38).
The complaints, which have been relatively high for a year, were primarily the result of a new billing system.
"In recent months, we have let many of our domestic customers down and I wanted to write to each of them personally to say sorry," said Npower's chief executive, Paul Massara.
"We have been in discussions with [regulator] Ofgem and are working on this as our top priority. Although we've made good progress fixing many of the underlying issues, we still have a long way to go, and our customers deserve to get the best possible service."
He said that customers would not lose out financially as a result of the problems. Meanwhile, the company said it would add an extra £1m to its Health Through Warmth Scheme Crisis Fund. This fund supports vulnerable homeowners with cold related illnesses who need heating repairs and installations that they cannot afford themselves.
The regulator has welcomed the move, having raised concerns about the issue although it had not opened a formal investigation.
"Many Npower customers will have noticed a serious deterioration in service levels over the last year," said Sarah Harrison, of Ofgem.
"We are pleased to see Npower's leadership team focusing on this issue, acknowledging the scale of the problem and sharing with customers its action plan to put things right."
Npower is not the only energy company to face problems over high complaints levels. The regulator still has an extended investigation open into EDF Energy's complaints handling processes.