The UK’s three biggest mobile operators are failing to offer their customers satisfactory service despite often costing more than smaller rivals, a watchdog has found.

Vodafone was rated the worst network in the country in the Which? mobile satisfaction survey after only managing one-star ratings for customer service, value for money and technical support.

One in five Vodafone customers (18%) reported poor customer service, including complaints handling and the way their queries were dealt with, while 13% said the firm’s technical support was poor and 19% rated it as poor value for money.

EE, the UK’s largest mobile network, also continues to rank among the worst providers, with 13% of its customers rating it as poor value for money, and just a quarter (27%) giving it a good or excellent rating for technical support.

Some 10% of O2 customers said the company provided poor value for money.

Three achieved the highest customer score among the “big four” networks for the fourth year running, despite receiving average scores in most categories.

However, 80% of Three customers rated their provider as good or excellent value for money.

Of the 13 providers included in the survey, customers mostly rated smaller “virtual networks” – those that lease spectrum from the main operators – more highly, with Which? finding that they were usually cheaper for both sim-only and certain contract deals.

Sim-only deals were on average 31% – or more than £3 a month – more expensive with one of the big four providers than with one of the smaller virtual networks.

The combined average monthly contract price for an iPhone XS was 18% or £10 more expensive with Vodafone, O2, EE and Three.

Which? singled out giffgaff as a provider popular with its customers, with 80% paying less than £10 for their sim-only contract and 95% rating the firm as good or excellent on value for money.

From July, all mobile customers will be able to switch provider by text message and firms will be banned from charging for notice-periods running after the switch date, a practice that is currently costing those caught paying for old and new services at the same time around £10 million in total each year.

Natalie Hitchins, Which? head of home products and services, said: “The continuing reign of smaller networks over the big players goes to show exactly how important customer support and value for money are to mobile users.

“If you think you are paying too much or are not getting the level of service you expect from your provider you should shop around for a better deal – you might find you save yourself some money and probably a lot of grief too.”

Vodafone said: “We are sorry that Which? members aren’t as happy as they could be with our service and are working hard to understand the issue and what more we can do.”

An EE spokeswoman said: “We’re ranked top by OpenSignal for mobile experience in the UK, which is supported by other independent reports from Ofcom and RootMetrics. Ofcom’s latest figures also show that EE receives among the fewest complaints in the mobile industry, as we’ve continued to invest in the UK’s best customer service.”

Which? surveyed 6,135 members in February.