O2 has received a surge in complaints after announcing last year that its new £2.50 monthly price rise for 2026 would apply to existing customers as well as new sign-ups.
The mobile provider had the most complaints in the final quarter of 2025, recording seven for every 100,000 customers, the latest data from the industry watchdog Ofcom showed.
That's more than double the industry average of three and seven times the rate of Three, EE and Tesco Mobile, which generated the fewest.
"The surge in complaints from O2 customers shows what happens if telecom providers undermine consumer trust for the sake of a brazen cash grab," said Rocio Concha, head of policy and advocacy at consumer group Which?.
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"The lesson for telecom firms is that consumers will not tolerate sneaky price increases, and they will call out bad practice."
Virgin Media O2 said: "On the mobile side, we understand customers were disappointed with our price change which led to a short-term spike in mobile complaints this quarter, and since then we have taken decisive action, including signing the government's Telecoms Consumer Charter."
Ofcom also released data showing the number of complaints filed against broadband companies in the same quarter.
It found Vodafone received the most complaints, followed by TalkTalk.
Virgin Media and Plusnet had the fewest complaints.
Among pay-TV providers, TalkTalk came out with the fewest complaints, while EE had the most.
What did the companies say?
Tesco Mobile said it was "incredibly proud" to be recognised as one of the least complained-about mobile providers.
Virgin Media O2 said: "Over the past 18 months, we've delivered clear and sustained improvements in customer service, with complaints about Virgin Media broadband now the lowest of all providers which is a major achievement.
"We remain on track and committed to investing heavily to ensure we're consistently providing a great customer experience and excellent service."
TalkTalk said it was disappointed by the results, but that it was part way through an ambitious customer service transformation aimed at identifying and tackling the root causes of complaints.
BT, which owns Plusnet, said it was focused on consistently providing excellent customer service.
(c) Sky News 2026: O2 shoots to top of complaints league table - and customers have one major issue
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