The telecoms watchdog has launched its second probe into TalkTalk this year following complaints that it both missold fixed line telephone services and switched consumers to its service without their consent.
Ofcom expects the investigation to take about six months and, if the group is found to have breached regulations, it could face fines of up to 10% of relevant turnover.
TalkTalk has been in discussion with the regulator for some time over the issue. A spokesman told the Independent that, although there had been a "limited number" of complaints, the number had recently started "ticking up". "Occasionally, there will be such instances on a systems level or an agents level," he added.
But earlier this month, it also emerged that Ofcom had given the UK’s second largest broadband supplier a month to comply with its rules after finding that it had wrongly issued customers with bills for services that they had cancelled.
The watchdog had received more than 1,000 complaints about the issue, but TalkTalk blamed some of the problems on the difficulties it had faced in moving Tiscali UK customers off a billing platform in Italy. It has also been grappling with the legacy of different types of contracts that it inherited after buying Italian firm Tiscali’s UK operations last year.