TalkTalk, Virgin and Vodafone are all failing to hit the right note with customers, according to a new report on satisfaction scores.
Regulator Ofcom has revealed its figures on where customers are the least and most satisfied - based on the thousands of complaints it received last year.
It looked at broadband and phone networks - and who received the best and worst scores from their customers.
Overall, it said 83% of broadband customers are satisfied with their service, while 13% had reason to complain in 2018.
TalkTalk scored below the industry average on several measures, with its broadband customers less likely to be satisfied with their overall service and less likely to recommend their provider to a friend.
UK's biggest mobile phone firms failing on customer service - worst offenders
It found the provider's customers were also statistically more likely to have a reason to complain, less likely to have their complaint resolved on first contact, and less likely be satisfied with how their complaint is handled.
Across the industry, Sky broadband customers are the least likely to have reason to complain, and more likely to be satisfied with how their complaint is handled.
Elsewhere, Giffgaff and Tesco Mobile customers are the most likely to recommend their provider to a friend. Their customers also have above-average satisfaction with value for money (97% for giffgaff and 92% for Tesco Mobile, compared to an 87% average).
Vodafone customers, on the other hand, are less likely to be satisfied with value for money (82%), while Virgin Mobile customers have below-average satisfaction with how their complaint is handled.
Both companies are also less likely to resolve complaints on first contact.
Complaints to Ofcom about broadband firms fell by 23% last year, from 75 complaints per 100,000 customers on average in 2017, to 58 in 2018. Most companies ended 2018 better than - or broadly the same as - they started the year.
However, complaints about Plusnet – owned by BT – more than doubled in the last quarter of 2018. In that period, the company experienced issues with a new billing system it launched.
Broadband customers can now get automatic compensation when things go wrong
Meanwhile, complaints to Ofcom about mobile networks fell by 15% last year – from 20 complaints per 100,000 customers on average, to 17 last year.
Lindsey Fussell at Ofcom, said: “Shabby service can be more than just frustrating; it can have a big impact on people and small businesses who rely on being connected.
“When you’re shopping around for a phone or broadband service, quality can be just as important as price. This information can help buyers make the right decision.”
Today's figures come ahead of new easier switching rules for mobile customers which come into effect on 1 July.
The regulator has also set out plans to force firms to tell customers when their contracts are coming to an end, including the next best value deals available to them.
