Fed up with harassment

They are totally ***********, useless and uneducated. I have been handed over by ADT for an account that has been closed a year ago. We've asked numerous times for a breakdown of how they have arrived at the so called "outstanding balance" and the *********** idiots keep sending me a Statement with a balance total. Prove to me that I owe that money! Do you really think that you can bully me with your **** attitude to pay over for something I don't owe. They have no interest to investigate if funds are really due, no hell we are just to stupid to figure out how to reconcile an acc. Did they ask for proof of when services with ADT was canceled, no, we don't have the brain functionality to think that far.