A few years back I took out a contract with vodafone and the guy in the shop said I could have a bolt on that allowed me to cheaply call my g/f in America (long distance relationship) on a cheap rate.
Took the contract out, made some calls to the States, BANG, £1100 first bill.
Turns out the guy hadn't even put the bolt on, and had been sacked since I took it out.
Whilst disputing this, Vodafone put a default on my credit account, and since then, I haven't even been able to get credit with anyone, despite earning in excess of 25k in my job, I can't even get a mortgage, hp, loans, credit cards, etc. Even now, as the debt shows as 'settled', nobody will touch me.
They refuse to take it off, no matter what I say, and I think if I managed to track down the guy who sold me the contract, I would probably put him in hospital and do some time.