Telecoms giant Vodafone has become the most complained-about pay-monthly mobile provider after issues with a new billing system sent customer grievances surging.
Regulator Ofcom said complaints made to Vodafone surged to 32 per 100,000 customers in the final three months of 2015, up from 20 in the previous quarter.
This made it the only provider to have more complaints than the industry average of 10 per 100,000 customers.
It comes after Vodafone moved customers over to a new billing system at the end of last year.
Ofcom said complaints received about Vodafone related to billing, pricing and charges, as well as complaints handling and fault, service or provision issues.
Overall, Ofcom said total complaints across telecoms and pay TV fell in the three months to the end of December 2015.
But the pay-monthly mobile sector was the only one to see a rise in complaints after the Vodafone issues.
Ofcom is separately investigating Vodafone over its complaints handling procedures, while it is also conducting another probe into the supplier's sales of pay-as-you-go mobile services.
The latest Ofcom figures also revealed that TalkTalk received the most landline complaints, at 30 per 100,000 customers, while EE, Plusnet, Post Office and BT also continued to generate landline complaints above the industry average.
EE again attracted the most complaints for fixed-line broadband, while grievances about Plusnet, TalkTalk and BT remained higher than the industry average.
BT held on to its spot as the most complained-about pay-TV provider over the fourth quarter, although the numbers dropped to 15 per 100,000 from 25 in the previous quarter.
TalkTalk also received above-average complaints about Pay TV, at 14 per 100,000 customers.
Vodafone apologised to affected customers as it admitted it suffered "some problems" with the "highly complex" switch over of customers on to its new billing system.
But it said: "We are working hard to improve our customers' experience and more recent data is showing an improvement."
It has beefed up its customer call centre teams to help deal with complaints and resolve billing issues.
"We would like to apologise to any customer who has had an issue with our service," the group added.
Talk Mobile also saw an increase in complaints in the fourth quarter, rising to nine per 100,000 customers, although this is just below the industry average.
The regulator said it receives just under 300 telecoms complaints a day from consumers.
As well as its ongoing investigations in Vodafone, Ofcom fined Three UK £250,000 in October last year, and EE £1 million in July this year for failing to comply with rules on handling complaints.
It also has an open investigation into Sky and its contract cancellation practices.
Ofcom's latest figures on broadband complaints show that Virgin and Sky saw below industry levels at the end of last year.
But the entire telecoms industry is facing more stringent performance targets on customer service after Ofcom's recent Strategic Review of Digital Communications last month.
It outlined plans to introduce tougher rules on faults, repairs and installations, transparent information on service quality and automatic compensation for consumers when things go wrong.
Ofcom also wants BT to open up its Openreach network to competitors and concluded the UK must "do better" at rolling out superfast broadband and 4G mobile.