There's a scam doing the rounds that is costing people hundreds of pounds, after a random missed call is triggering outgoing calls from your account, which lasts for hours to a premium rate line.
Ofcom are looking into cases where massive bills have been generated thanks to scam called to 0845 and 0843 numbers.
These calls have included connections to claims management firms, and even though the call isn't answers, mobiles are still connected to the premium rate lines for up to 12 hours, with some people getting charged £300.
According to reports, the scam has been done on Vodafone accounts.
The mobile operator is currently blocking these suspicious numbers and refunding customers who have been scammed out of money.
An Ofcom spokesman said: “We are very concerned to hear of a number of people receiving mobile charges they didn't expect. Ofcom is working with the mobile operators, industry experts and partner regulators to establish the causes and address the problem."
"We are pleased that Vodafone is blocking suspicious numbers and refunding affected customers. We advise those who believe they are affected to contact their phone company promptly."
Vodafone says: "Vodafone's systems have not been compromised or breached in any way. Our security monitoring systems have identified that a number of customers have returned unsolicited calls, leading to them being charged significant amounts."
"We have taken proactive measures to ensure none of the customers affected are out of pocket and have identified and blocked the numbers creating this issue."