Continuous billing after cancellation

I sold my business in June 2014. On 16 July 2014 I wrote a letter to ADT cancelling my contract. The letter was hand delivered to the Kimberley branch office. Billing continued. I rep**** by email that the contract was cancelled with no response. In February 2015 I went to the Kimberley office, with a copy of the letter and asked the staff if the contract was cancelled as I requested. They assured me that it was cancelled. Billing continued.<br> Yesterday I received another statement. I phoned the 086 number on the statement, was given various automated options on the phone, held on for what seemed to be a lifetime, without any success. I phoned the Kimberley office, spoke to Tebogo, who remembered me. Tebogo assured me that she sent through the cancellation, but she has nobody to speak to at head office who will sort out the problem. Late yesterday afternoon I received a voice message from ADT with no solution. This is not acceptable and would like to know what ADT is going to do to resolve the matter