Debt recovery on moved broadband with BT (Current ...

Question

Small history:
Signed up with BT broadband some 3,5 years ago, As well as a phone line. About 1,5 year later, we moved address not to far from the old one, and thus called BT to have our phone and broadband moved to the new address.
I asked weather this was a problem, as we had run the course on our contract, and they didn't give any warning signs as to us moving to a new address.
As we held on to the old apartment for 2 months after moving to the new, not long after, they contacted us regarding an outstanding bill at that old address, and I asked how that was possible since we were now installed at a new address and paying for both broadband and phone there, and also why I was told that it would be closed, with no charges, when moving into a new address. One phone call later they were happy that to inform us, that it was a mistake, and the charges would be removed, we assumed that was the end of it, and continued to this day, with BT.
Now this morning, we received a letter from a Debt recover agency called SRJ. They claim we owe BT 150 pounds in outstanding charges for BT broadband at our old address. To be sure after calling them, talking to some person claiming this and that, not to mention the threats, I went to try and call BT and ask them what they possibly have going on here. Got India, and got disconnected (Will try to get an English number for billing if it exists) no surprise there (Anyone got a number to English "service" ?)
So, apart from the fact that I don't believe one second, that after 2 years, they suddenly pop out, with no warning to collect money, that we never owed them in the first place, as all bills have been and always was pay'ed. Any suggestions and or experience with similar claims would be appreciated.
Cheers, Mac,

Answer 1

Update.
About 2:30 into calling BT, and 2 wireless phones with dead batteries later, on the 4 call, I managed to get through to the correct department for billing in the UK. Spoke with a very nice lady, who promised that they would call of the debt recovery, until the matter had been sorted, and is now being looked into, with a firm promised that she would call me back within the day, to see what they can recover.
As this is on the old account system, they seem to be having trouble accessing the details, but I did manage to attain, that they believe to have somehow transferred back a valid payment of our broadband, to our account, thus missing a payment from May 2009.
This brings me back to the fact, that our broadband contract at the old address ended in January or February 2009 and we took over the new address from 2nd of march 2009. I even have a letter from the 26 February stating that they are happy to confirm the renewal of our old contract, which makes no sense, and probably where the fault lies, as I remember calling them asking why they are renewing our old contract when, we in fact, just asked them to move the broadband to our new address a week later. This is where they returned payment we made via direct debit probably around may 2009 where that bill would have been due.
Going to check into our accounts, if they date back that far to see what has been payed and what was returned and when. Might shed some light on this rather odd occurrence.