Poor Customer Service

I used to be a customer with ADT for approximately 12 years, never skipped payments. I gave sufficient notice to cancel my membership . They never collected their radio or communicated with me to collect. I had no communication regarding an outstanding amount of 392. No I get a thread that my credit score rating may be affected because of non payment. When I phoned the company that ADT handed me over to, they didn't even had the correct email address for you. They had my work email address from when I joined over 12 years back. I got no communication via telephone, nor email that I owe ADT money. I think this is very poor client services and ********* to try and black list people if you own inhouse accounts department couldn't even to contact me. Please may the Head of ADT SA respond