Thanks, Buzby and the others who have responded. You were right to advise against phoning - despite three more calls to them, the harrassment has continued and today they have passed my account to a debt collection agency. That's just ONE WEEK after their warning letter - so if I had been on holiday, say, I would have come home to a very unwelcome surprise. Each time I have spoken to T-Mob, they have assured me that my account is closed and/or no further action will be taken. But presumably because it's just a phone call, they feel happy just to ignore it and keep chasing me. Experian were more helpful and have now placed a note on my records, which should mean that any check on my credit rating will throw up the fact that I dispute it. But I'm pretty sure that T-Mob didn't check in this case, so probably some [EDIT] will get away with it again. I will be also placing my records in Protective Registration with CIFAS. Not sure what good this will do, apart from making my own life a bit more complicated, if companies don't even bother to check. However, I'm wary of doing anything which might be seen to be an admission of liability I'm getting really angry with T-Mob about this. Not only for myself, although it's a big hassle, but because similar things must be happening to many others, who might, for example, be in the process of applying for a mortgage, changing jobs, or some other major life event, and this would cause them enormous problems. And do T-Mob care? There are real lives being harmed by their incompetence.

Thanks, Buzby! I certainly don't want to make myself appear complicit with the fraud. I have already checked my credit files, and, yes, the "account" does appear there. Currently it shows £34 in arreers but unless this is sorted out, it will no doubt soon show missed payments and all sorts of bad things and seriously affect my credit rating. I have written to Experian (email, actually) but there are other credit agencies, and IMHO it should be T-Mobile who have to sort it out. Any advice about whether I should play along with T-Mobile's request to fax my passport and proof of address would be welcome.

I am having an experience very similar to Addled. Some b** has opened a mobile account in my name and got a £240 Blackberry on the back of it. I have called T-Mobile at least four times and each time get more stupidity from them. The first I knew about it was mid-December when I got a "Welcome to T-Mobile" letter. I immediately called them, and a few days later I got another letter saying they were sorry blah blah blah and that they had cancelled the phones from my account and would not link the phone to my account. BUT I don't HAVE an account with T-Mobile, I have never had an account with T-Mobile, and I certainly will never in the future have an account with T-Mobile. At first they were sympathetic but not very helpful. They did however suggest that I should report it as an identity theft crime with the police. Stupidly, I did not do this right away, since I really believed T-Mobile when they told me that the account was closed and I wouldn't hear anything else. But, so far from cancelling the account, they have continued to harrass me for payment in a way which is, frankly, immoral, unfair, and probably illegal. Now they have threatened to hand the "debt" (which of course I don't owe) to a debt collection agency, pass the details to credit reference agencies, and continue to charge me for the remainder of the agreement (which I never entered into in the first place). When I called them, they told me that the account is now in the hands of "Collections" - that is, NOT in the fraud department at all. It seems that T-Mobile find it more convenient to hope that I will simply give in and pay someone else's bill. But to do so would be to admit liability, and I am certianly not liable. I have now finally reported the identity theft to the police. As soon as I have some report back from them with a crime number, T-Mobile will be getting a very stiffly-worded letter. I am also in the process of raising the matter through the Communications and Internet Services Arbitration Scheme (CISAS), although they will probably want me to wait until T-Mobile have had a chance to sort it out themselves - I believe CISAS normally want 8 weeks from an initial complaint before they will intervene. I have asked T-Mobile for details of the agreement which some thief has presumably signed with them, but they refuse to give it. I might have to make a Subject Access Request under the Data Protection Act, but this, too could be seen by them as an admission of liability. T-Mobile insist that the phone was delivered to my home address - which it clearly was not. At the same time as refusing to give me the information which I need to prove my innocence, T-Mobile want me to fax them a photocopy of my passport and a utility bill with my name and address on it to their fraud department. They seem to think that I am the one under investigation and that I am supposed to prove to them that I am entitled to this phone and account. But I don't HAVE this account, I don't have their phone, and I don't WANT it. I am also very wary of sending them anything which might 1. be taken as an admission of liability and 2. could be used by [problematic], since there could be insiders in T-Mobile. I really don't like the idea of sending personally identifying details to a fax number which I cannot trace and which could easily be intercepted. I'd love to hear how Addled got on with his/her case - I'll let you know how I get on with mine.