TalkTalk has been named as the most complained-about broadband firm in the UK, according to the latest report from regulator Ofcom.
The watchdog received nearly 250 complaints a day about communications services from July to September 2017.
The Post Office came out worst for landline services and Vodafone received most complaints from mobile users.
In response, TalkTalk said closure of customer service centres in India had been partially to blame.
"That move, and a radical shift to self serve, is already delivering a material improvement in customer satisfaction and we expect complaint data for 2018 to reduce significantly," the firm said in a statement, adding that it was "disappointed" by the figures.
TalkTalk and BT received the worst customer satisfaction scores in a survey of 12 broadband providers, conducted by Which last year.
According to Ofcom, the main sources of grumbles against TalkTalk were faults, service and provision issues. Complaint handling and billing were secondary concerns.
The industry average for complaints about broadband was 18 per 100,000 people, Ofcom said.
- TalkTalk had 30
- Plusnet 27
- BT 25
- Virgin Media 14
- EE 10
- Sky 7
In the landline market the worst provider was the Post Office, with 24 complaints per 100,000 customers, although many of the issues were attributed to its takeover of Fuel Broadband, which led to problems with service provision and complaints handling.
In the mobile market, Vodafone came out worst, with 10 complaints per 100,000 customers. By contrast, BT received nine, EE, Three and O2 all had three while Tesco only recorded one.
Jane Rumble, Ofcom's director of consumer policy, said: "We're shining a light on how different providers perform, and it's clear many need to up their game on service quality and complaints handling.
"People expect high standards from their providers and companies must put their customers first."
Ewan Taylor-Gibson, telecoms expert at price comparison site uSwitch, said: "If we take a longer term view, the overall trend is that complaints to Ofcom are continuing to drop, which hopefully suggests providers are improving their service delivery rather than consumers being less minded to complain.
"Having said that, there are still areas that could do with some improvement - customers are still most likely to grumble about broadband and landline services."