Virgin Media is being investigated over complaints the telecoms provider is making it difficult for customers to cancel their contracts.
The media regulator Ofcom said it was concerned by the number of complaints it had received from Virgin Media customers who had tried to leave but said the company had made it difficult for them.
Some said they struggled to get through to an agent on the phone, some found their call was dropped mid-way through or they were put on hold for long periods, and many said they had to make lengthy and repeated requests to cancel, after noticing their contracts were still running.
Ofcom warned being able to switch provider easily was an important part of a competitive market, particularly during the current cost-of-living crisis, and confirmed that it will now investigate whether Virgin Media is putting "unnecessary barriers" in the way of people who want to switch providers.
Virgin Media said it will comply with the investigation, and complaints relating to "difficulties leaving" had halved over the past year.
The investigation comes as the regulator announced plans to highlight the telecoms firms which aren't offering the cheapest deals for vulnerable customers.
Ofcom chief executive Dame Melanie Dawes wrote to the bosses of the major providers to call for immediate action on cheaper social tariffs for those claiming Universal Credit, Pension Credit and some other benefits.
Ms Dawes has urged providers who are yet to introduce a social tariff to do so “as soon as possible”.
Ofcom said it will publish take-up of social tariffs by providers for the first time in its annual pricing trends report, due later this year.
Ms Dawes said: “We’re taking action today, on behalf of Virgin Media’s customers, to investigate whether the company is putting unnecessary barriers in the way of those who want to switch away.
“We’re also expecting more from the industry as a whole in helping to support customers through the cost-of-living crisis. That means no more excuses when it comes to offering and promoting social tariffs to eligible customers who could switch and save today.”
A Virgin Media spokesperson said: “We are committed to providing our customers with excellent service, supporting them with any issues and giving clear options should they wish to leave.
"Complaint rates relating to ‘difficulties leaving’ have halved over the past year, showing the progress we’re making, and we will keep working with Ofcom throughout its investigation, while making further improvements in how we handle customer complaints to provide a better overall experience.”
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