The number of people complaining about their broadband service is on the rise, according to the regulator.
There were 20 complaints for every 100,000 customers in the three months to the end of September, up from 15 in the previous quarter according to the latest complaint data from Ofcom.
BT topped the naughty list with 36 complaints per 100,000 customers, followed by BT-owned Plus-net with 30 and EE with 26.
The new figures come amid the regulator's scrutiny of BT's Openreach business, which chairman Mike Rake admitted had not been good enough in the past. Ofcom is forcing BT to split its Broadband business.
Complaints about landline providers are also on the rise. Plusnet and EE were also found to have had the most complaints - 24 and 20 in every 100,000 respectively, compared to an average of 14.
The date is compiled to give consumers better information when choosing service provider or when switching. It is also aimed at incentivising firms to provide better customer service.
“We won’t stand for complacency when it comes to customer service. We expect providers to make it a top priority and work hard to better serve their customers," said director of Ofcom's consumer group Lindsey Fussell.
“If companies let their customers down, we will step in and investigate which can lead to significant fines."
The rate of complaints around mobile and pay TV has fallen.
In terms of mobile provider, Vodafone was the most complained about company with more than twice as many gripes as average - 18 versus six in every 100,000 customers. However, its the third consecutive quarterly decline for the firm which was slapped with a multimillion pound fine by Ofcom in October over customer failings.
BT was also the most complained about pay TV provider with 19 complaints per 100,0000 customers, compared to an average of four and 15 the previous quarter.