TalkTalk has come last for the second year running in a broadband service report released by regulator Ofcom.
The company's customers were the least likely to recommend their provider to friends. It scored poorly for reliability and complaints handling.
A company spokesman said that while the "results are disappointing", TalkTalk was rolling out major service improvements.
Virgin Media had the most satisfied customers for broadband speeds.
TalkTalk said: "We've closed down our call centres in India. We have introduced new online tools to help customers resolve issues quickly and conveniently. And we are launching new Wi-Fi routers to strengthen network reliability.
"All these initiatives are starting to deliver material improvement in satisfaction levels."
The report covers the quality of service broadband users can expect from the UK's six biggest providers.
It is part of Ofcom's efforts to encourage consumers to "shop around" for providers that best meet their needs.
Overall, eight in 10 broadband customers said they were satisfied with their service, while 15% had a reason to complain.
Virgin Media was the only provider with above-average customer satisfaction for broadband speeds. And its customers were more likely than average to recommend it to a friend.
The report also highlighted that across the industry, satisfaction with complaints handling could be improved.
Members of the public were also questioned about the mobile networks they used.
Overall, nine in 10 customers (91%) said they were satisfied with their mobile providers, with just 4% having a reason to complain.
Among the mobile providers, Vodafone and Virgin Mobile customers were least likely to recommend the services to others.
Tesco Mobile and Giffgaff fared best on the same measure.
"People often focus on price when they're choosing a phone or broadband provider, but there are big differences in the customer service offered by providers," Lindsey Fussell, Ofcom's consumer group director, said.