Which broadband, landline, mobile and pay TV firms receive most complaints?
TalkTalk is the most complained about home broadband and landline provider, while BT and Vodafone drew the most complaints for their mobile services, figures show.
BT is also the most complained about pay TV provider, according to the latest quarterly league tables of complaints made to Ofcom from October to December.
Faults and other problems with TalkTalk's broadband and landline services led its customers to send it to the top of both complaints tables.
TalkTalk drew 31 complaints per 100,000 customers, followed by BT and Plusnet on 27 - all well above the industry average of 18.
TalkTalk also attracted 23 complaints per 100,000 customers for its landline service, again well above the industry average of 13.
In a poor quarter for BT, problems with its complaints handling, billing and charges for both its mobile and pay TV services saw it top the league tables for both - tying with Vodafone for complaints about mobile services with 11 complaints per 100,000 customers for mobile compared with an industry average of five.
BT's pay TV offer drew 18 complaints per 100,000 customers, above the industry average of five and best performer Sky's two.
Broadband and landline services continued to generate the most complaints, but the overall volume remained broadly in line with the previous quarter, the regulator said.
Jane Rumble, Ofcom's director of consumer policy, said: "These figures give people the information they need to shop around and compare providers' performance.
"The scorecards also motivate companies to improve their performance, and we want to see them follow through on their promises to give customers better service."
A TalkTalk spokesman said: "We always strive to provide the best possible experience and are disappointed by these results.
"Ofcom's historical data reflects a short period last year which coincided with the closure of our contact centre in India.
"The move was part of a major investment to improve our services but caused some temporary disruption for customers."
A BT spokesman said: "We're really disappointed that complaints have increased this quarter.
"We know we can do better, which is why we're investing heavily to improve our customer service."
The best and worst providers by service, according to number of complaints per 100,000 customers, are: