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Vodafone has been rated the worst mobile phone provider for the seventh year running in an annual customer survey by consumer lobby group Which?.

The other leading providers, EE, O2 and Three, also scored badly, with service judged "average" and "disappointing".

Of the small providers, Utility Warehouse ranked highest for value for money, incentives and customer service.

Vodafone said improving services for customers was a top priority and it had been working hard to address the issue.

It said in a statement: "These findings published by Which? really don't match up with what our customers are telling us, with our own, independently verified customer satisfaction scores jumping 13 points from last year to their best ever level."

The survey by Which? asked 3,600 consumers about their service provider.

Wrong bill

The smaller networks that use the big four's infrastructure, known as mobile virtual network operators (MVNOs), beat the big four on customer satisfaction and the likelihood that users would recommend the service to a friend.

Vodafone had the worst customer score (49%) with one in six customers telling Which? they would not recommend it to a friend, compared with nine in 10 Utility Warehouse subscribers who said they would recommend their service.

One in seven Vodafone customers also said they had received an unexpectedly expensive or incorrect bill, Which? said. The network was also rated worst for customer service.

EE finished second from bottom. One in seven of the EE customers surveyed pay more than £50 a month for their contract, and Which? said it was not surprised that the service received a low score for value for money.

Switching provider

Alex Neill, from Which?, said: "Customers who are fed up should look to switch provider as soon as they can."

She pointed out that new reforms would soon mean that mobile customers would be able to switch provider by text message.

Ms Neill said: "We hope [this] will make it quicker and easier for customers to seek a better deal."

Last week, media regulator Ofcom said that Vodafone and BT, which owns EE, were the most-complained about mobile operators in the final three months of last year.