The sponsor of The X Factor said that its overall broadband user numbers slumped by 43,000 in the three months to September 30, following another fall in the previous quarter.
TalkTalk, which today confirmed plans to trial digital TV service YouView in the first quarter of 2012, also said that it expects customer numbers to continue falling in the second half of its fiscal year (running to the start of April 2012).
Underlying profits at TalkTalk increased 20.7% to £146 million in the six months to September 30, as the company saw the benefit of higher margins from moving broadband customers over its own network via a local loop unbundling programme.
However, the company and its Tiscali UK division was fined £3 million by media regulator Ofcom in August for wrongly billing tens of thousands of customers for services they had actually cancelled. This was also despite the group already paying out around £2.5 million in compensation to affected customers.
TalkTalk chief executive Dido Harding said that improvements to the company's customer service operation had resulted in a 40% reduction in the number of calls to call centres, while 75% of queries were now being resolved straight away.
She admitted, though, that there was a "lag" between the improvements in customer service and an increase in customer numbers, although she is "confident that the effects will soon become more apparent".
Watch a video of Harding discussing TalkTalk's results below:
Harding expects the company's broadband customers to return to growth in the first half of the 2012/13 financial year, following a modest decline in the current half-year to April.
Revenues in the first half of TalkTalk's financial year declined 5% to £844m but Harding said that they are expected to be "flat" in the second half. Shares in the group were down 2%, despite the announcement of a 53% increase in its dividend to shareholders.
In a statement, Harding said: "We are pleased that we are delivering a better experience for our customers, demonstrated by the continuing reduction in calls into our contact centres and a significant increase in the number of customers' queries being resolved first time.
"This reflects our priority to improve customer experience and make our end to end systems and processes both more effective and more efficient. There is a lag between these initiatives and improvements in customer numbers, but we are confident that the effects will soon become more apparent."
She added: "We continue to be the best value provider, with more of our customers saving money by buying more products from us and we are making significant progress on upsell to Plus, Homesafe and Boosts.
"The launch of YouView next year will be a major development for TalkTalk and we are on track to offer a value for money product of phone, broadband and TV in spring 2012."