Debt collectors chasing me for an account that was...

Question

Hello all,
Received a phone call this afternoon from quite an aggressive lady from a company called Advantis and representing a third party called TDX.  She was quite cryptic at first and started out by asking me for lots of my personal details.  I went along with this for a while then decided I had had enough and I wanted to know what was going on.  
She informed me that I owed (either her company or TDX, I'm not 100% sure as I had just woken up) for an outstanding BT bill of £197.  I told her I thought she must have made a mistake but she was not interested and just wanted to talk about payment.  She wasn't even able to give me exact dates or even the reason for the charges but did inform me that she worked for a debt collection agency.
I told her I would commit to nothing until I rang BT.  I got through to the BT call centre about an hour later and was indeed told I had owed broadband and line rental frees from July, August and September 2010 that they having tried to collect from me unsuccessfully had sold onto a collection agency.
I'm not currently a BT customer - I cancelled my last account with them at the end of May 2010 as I was moving house.  I told the call centre advisor this and he admitted that he could see on my account a phone call I made on the 29th May 2010 to cancel my account.  I had at that point paid the following months (June) fees.
However he then informed me that the cancellation had been cancelled!  He did not tell me by who though.  I assumed this was just a minor problem and he would be able to see that my usage (MBs) of the service ceased at the end of May and obviously a mistake had been made cancelling the cancellation.  I never used a phone from this line so it was all just rental and broadband.  He sounded positive that a favourable outcome could be arrived at but he would have to ring me back in 30mins.  Hate these ring back promises as I've been lied to in the past by some BT reps.
He did ring back, after an hour, but did apologise for this so I was happy enough - the conversation started well but then he informed me that the service had been used as he could see data totals for 3 months after I left my address.  I asked him how this was possible as I had moved out of the property and he basically said this was only possible if I had still been living there and using the service.  He basically implied I was lying and would have to pay the bill with the third party.
I have a letter from the company I rented the flat from informing me that I had given notice on the flat in April 2010 and would have to move out at the end of May - If I was still there and using the service I'm sure the new tenants would have spotted me!!!
I was then informed again that this was my debt and he could do nothing for me and I would have to pay it.  I re-iterated that I had left the address at the end of May and asked if there was any possible way this could have happened by accident - he said no the account must have been accessed by me or somebody who knew my password and from my flats landline!  I had never told anyone my password.
The account was finally cancelled after three months of non-payments and I was told they will have tried all ways of contacting me - nobody thought to Email me at my 10 year old BT Internet account though!
He ended the call by saying his manager would ring me in 2 hours time, 3 1/2 hours have passed since then!
From what I have read this seems like a friendly forum - If possible could anyone comment on the following please:
How and why would a cancellation be cancelled?
When investigating this before sending to debt collectors did nobody see the cancellation on my account and notice that my direct debits had been cancelled and think it was a bit odd?
How can my account run up data usage when I no longer lived in the flat or used the router or landline - I had moved 200 miles up the country and was using a Virgin service?
Does this cast doubt on the amounts of data I was being billed for prior to the cancellation, some of my monthly bills were very high?
Is my credit rating now trashed?
Why do BTs overseas call centres only ring back 50% of the time?
Sorry its so long but I wanted to give as much info as I could, hoping for opinions

Answer 1

Nobody from the call centre bothered to ring me back as promised yesterday.
I waited until 12.45 today to ring them again - spent 15 minutes on the phone explaining again to be told the they were having system problems and couldn't help me.
Was again promised a call back - 8 hours later still no call back!
If the debt collectors ring again I'm reporting them to the police and BT to the Office of Fair Trading.
If anyone from BT does read this can I have a job in one of your offshore call centres please - it sounds great, just keep promising callbacks that you never have to make!