Mobile phone customers are being warned about a sophisticated new scam which could cost them hundreds of pounds.
Communications regulator Ofcom is investigating the fraud which sees users receive a missed call from an 0845 or 0843 number - then get billed up to £300.
Despite not answering or returning the call, Money Mail says users are somehow being charged for chats lasting up to 12 hours.
Ruth Dance, from Berkshire, was charged £300 after being called from 0843 9800 146. Her network provider, Vodafone, insisted Ruth must have made the call, which lasted over nine hours.
Another woman, Diana Dentith, from Suffolk, said her usual monthly bill of £9 rose to £375 after she missed a call from 0845 429 0015. Also a Vodafone customer, Diana said she was originally told that she must have called the number for 12 hours.
Vodafone has now reimbursed affected customers and 'identified and blocked the numbers related to the fraud'.
Ofcom said this is an industry-wide problem and not confined to a specific network.
An Ofcom spokesperson added: "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 advise those who believe they are affected to contact their phone company promptly."