ADT / Norman Bisset

I had a contract with ADT which was cancelled, correctly after their 24 month period. Only to find that their sales person took out a second contract in my name when I moved residence. I have an email from the ADT accounts department stating that this second accounts payments were suspended. I thought that was the end of it. The account was duly handed over to Norman Bisset for debt collection after trying for months to get in touch with ADT. How can I resolve this? I had one phone call from Norman Bisset, and I was told that a consultant would be in touch, this was 3 weeks ago. I've tried making contact again but have not recieved much more than a statement which has the debt on it only increasing.

Please can someone get in touch with me so that I can sort this out before it affects my credit score.