ADT pathetic and thieving

We cancelled our ADT account when we moved in the correct manner sending all documentation etc required on the 18th of November 2017. To this date (23/06/2018) we have resent all documents twice already and have been receiving constant debit orders,smses and calls from them asking for money. We need to reverse the debit order every single month. They are *****ing money for a service that has been cancelled 7 months ago and is not being used any longer. Pathetic service and thieving.