A record £20.7m in compensation was paid to broadband customers who used a new scheme to complain about their service in the last six months of 2019.
The scheme, which does not necessitate formal claims, paid out for delays in repairs and setting up new connections and missed appointments.
Ofcom said just £8m was paid to customers in the first six months of 2019, before the scheme was introduced.
Yet 85% of customers were reportedly satisfied with their broadband service.
The watchdog's annual report showed Plusnet customers to be the most satisfied with their broadband - and TalkTalk users the least.
Nine in 10 mobile mobile customers said they were happy with their phone service.
Tesco Mobile users reported higher-than-average satisfaction levels, while Three customers were the most dissatisfied, reporting the longest call waiting times and worst reception.
Ofcom's consumer group director, Lindsey Fussell, said: "Checking the quality of a phone or broadband provider's service can be the difference between you signing up to a company that keeps you connected or one that falls short."
The data looks at how providers performed up to January 2020, so does not cover the Covid-19 pandemic.
Ofcom is hailing the new compensation scheme, which it introduced in April 2019, as a success.
The payouts include:
- £9.7m for delayed repairs following loss of service,
- £1.6m for missed appointments
- £9.5m for the delayed provision of new services.
Under the voluntary scheme, customers receive compensation from their provider without having to ask for it.
BT, Sky, TalkTalk and Virgin Media are among those who have signed up, and Ofcom is urging other providers to join to ensure "customers get fair compensation when things go wrong".