Handed over yet no account for almost 3 years?????

The incompetence of ADT knows no bounds! I cancelled my account nearly 3 years ago and sorted out all payments with them yet on Friday i receive an SMS that i have been handed over for my account not being paid!!! How the hell is this even possible and how dare you hand me over when i have no account, let alone statements. What makes it better is that the Phone number they give me to call to query doesnt exist!!!! I suggest someone contacts me IMMEDIATELY to get this sorted out for once and for all as i never want anything to do with ADT as you clearly are useless and if this affects my credit record i will not take this lying down.