The telecoms operator TalkTalk lost 25,000 subscribers in the third quarter, but said higher spending by existing customers meant it was still on track to hit its full-year targets.
Thousands of people switched provider after problems arose as TalkTalk attempted to bring over customers from Tiscali – the rival it bought in 2009 – on to its billing systems.
Morten Singleton, an analyst at Panmure Gordon, said the loss of clients was concerning "while both Sky and BT are making significant progress with about 200,000 additional customers each". The chief executive, Dido Harding, remains focused on cutting costs and integrating the two businesses, and Mr Singleton said he believed the company was being prepared for sale.
The news came a week after TalkTalk, which demerged from Carphone Warehouse last March, said it would shed 580 staff as part of the consolidation with Tiscali.
Ofcom has officially warned TalkTalk that it could be fined for its billing problems. Some customers are still being charged for services they have cancelled, and the regulator warned in November that the company faced enforcement action if it persisted.