BT, Plusnet and TalkTalk were the most complained about broadband providers during the fourth quarter of 2016, Ofcom has revealed.
According to new figures from the regulator, the total volume of complaints it received about telecoms providers overall went up between Q3 2016 and Q4 2016.
However, broadband and fixed line services continued to account for the biggest proportion of complaints regarding the industry during this time.
BT was the most complained about broadband provider towards the end of 2016, with 33 complaints per 100,000 subscribers between October and December.
Plusnet was not far behind, with 30 complaints per 100,000 subscribers, while TalkTalk racked up 29 complaints per 100,000 subscribers.
EE also fared badly in the data, with a figure of 26 complaints for every 100,000 customers.
However, some major broadband providers did perform relatively strongly throughout the quarter.
Virgin Media was the subject of just 13 complaints per 100,000 subscribers, while the figure for Sky was eight complaints per 100,000 customers.
These two companies performed much better than the industry average of 21 complaints per 100,000 subscribers.
However, this figure is slightly up on the average of 20 complaints per 100,000 people recorded in Q3 2016 - a possible cause for concern across the entire broadband industry.
Lindsey Fussell, Consumer Group Director at Ofcom, said: "Providers must get on and deliver consistently excellent customer service, and we expect this to be their number one priority.
"When companies get things wrong, we won’t hesitate to investigate and potentially levy fines."
Responding to the figures, a Sky spokesperson said: "Sky has generated proportionately fewer Ofcom complaints in broadband, talk and TV than anyone else during the past year, but we always set ourselves higher standards.
"At Sky, we are constantly trying to innovate and make things easier for our customers. We’re focused on providing this same high level of customer service to our mobile customers."
BT responded to the data by insisting it cares about the service it provides and is investing heavily in making improvements.
Speaking to Mirror Money, a spokesperson said: "We’re on track with our plan for 90 per cent of our customers’ calls to be answered by advisors in the UK and Ireland, which involves recruiting more than 1,500 people.
"We’ve invested in a major upgrade in the software our call centre advisors use, which is also enabling more customers to serve themselves online.
BT said customers will see an improvement when these initiatives take effect and pledged to start publishing its key customer service improvements on its website, so customers "can track the progress for themselves".
A spokesman for Plusnet added that it is "disappointed" with Ofcom's results, as it wants the best for its customers.
However, he said the company is "determined to improve" and has been working on "a number of changes to make this happen".
"We’re committed to doing our customers proud," the spokesman added.
The release of the data comes shortly after Ofcom proposed new regulations which would require telecoms firms to automatically pay out to customers if they experience missed deadlines, slow repairs, or if an appointment is not kept.
The regulator believes this could result in as much as £182 million in extra compensation being paid out annually, with households set to get £30 if they wait in for an engineer, only for them to fail to arrive or for the appointment to be cancelled at short notice.