Energy supplier npower has seen its profits fall 65% as it struggles with billing problems.
Its parent company RWE said the Big Six firm’s retail energy supply business saw a steep decline to £38 million in the first half of 2015.
That’s down from £109 million in the same period last year.
Its generation and retail business made a combined profit of £24 million in the first six months of 2015, a £11 million fall from the previous year.
npower said one of the main reasons for the decline in the domestic business is the “continued impact” of the customer billing system and process problems.
The Big Six supplier also lost more than 300,000 customers in the past year.
It follows the Energy Ombudsman ordering npower to provide free energy to those customers who waited too long for the company to deal with their complaints.
It has been one of the most complained about energy suppliers this year.
Paul Massara, CEO of RWE npower said: “The first half of 2015 has been very tough for npower’s domestic business, even though this has been balanced by the continued improving performance of our other businesses. We have continued activity to make sure all of our domestic customers are on the right product for them, meaning more than ever are taking advantage of cheaper, fixed length deals.”
He insisted the company has made “real improvements” and complaints have fallen to the lowest level since December 2011.
The UK supply unit accounts for 6% of RWE’s business.
RWE’s operating profit from green energy however soared in the first six months of this year.
Its renewables division RWE Innogy’s profits hit €233 million (£166.5m) during the first half of the year, up from €81 million (£57.9m) in the same period last year.