contract term but handed over a year later

Hi,my name is Mr S pillay(***)I did have a contract with adt security,but ended in 2014,received confirmation of cancellation etc,thereafter no correspondance from adt(used to receive statements in the post every month)got an sms more than a year later saying I have been handed over to debtsource oweing monies to adt.shocked,if I had owed monies to adt,why didn't adt correspond with me their customer saying I owe monies but instead they have handed me over to debtsource with no correspondance and with out my knowledge more than ayear later,absolutely perthetic,will explore my legal options.disgruntled customer.adt supposed to be providing a sense of security,this makes me wonder about their organisation,capable or not capable.Regards S Pillay