Cashback deals from mobile phone providers are a "rip-off" and should be banned, it has today been claimed.
Which? says the deals, which see customers pay upfront for a contract and handset and claim money back over a period of time, "sound great but are highly dubious".
According to the consumer watchdog it has received thousands of calls from people saying they are not able to claim their cash back.
This is reportedly due to the terms of their deals being overcomplicated or the firms themselves going insolvent.
"We think mobile phone cashback deals that make customers jump through hoops to get their money should be banned. If cashback is offered, it should be automatic," said which.co.uk editor Malcolm Coles.
"Thousands of people have already lost money through these dodgy deals, so dont touch them with a bargepole. Ring in the new year with a cheap mobile phone deal that doesnt include cashback."
Two months ago mobile phone giants O2, Vodafone, 3, Orange and T-Mobile promised to oversee the cashback offers in an Ofcom-endorsed voluntary code of practice.
But Which? says it has checked ten mobile phone dealers' websites and found the code breached in six places.
O2 and Orange have vowed to change the offers immediately, while Vodafone said the code was in its "infancy".