******* handing over of a non existent ADT account

I used to have a contract with National Fire and Security which was cancelled prior to ADT taking over National Fire and Security. After ADT took over National Fire and Security I received a call from someone at ADT to let me know that ADT had taken over National Fire and Security and that I needed to cancel my contract with ADT. I explained to the person that my contract was never with ADT, that it was with National Fire and Security, and that my contract with National Fire and Security was validly cancelled BEFORE ADT took over National Fire and Security. DESPITE not having a contract with ADT, ADT has handed my NON EXISTENT ADT account to debt collectors (Norman Bissett and Associates) who continue harassing and hounding me to pay an amount which I DO NOT OWE. This is pure harassment, and shocking behaviour on the part of ADT and Norman Bissett and Associates (I have advised Norman Bissett and Associates on more than one occasion that I DO NOT OWE ADT any monies!)