Contract cancellation never actioned

In October of 2013 I cancelled my contract with ADT as I was no longer able to meet their monthly installment. In December of 2013 they sent me a Statement with the outstanding payment for November and December, I responded via e-mail to inform them that I had cancelled this contract in October already. The Agent who then contacted me after that informed me that they seemed to have missed that e-mail cancellation or something of that sort, the Agent then try to keep me and not to cancel the contract. I informed them that I was not in a position to commit to this so they should cancel the contract. in March of 2014 they were still sending me a bill for the service that was cancelled. Later in September of 2014 I got a call from one of the Agents stating that my account is in arrears, almost a year after the contract was cancelled. In February this year I got an SMS from Debtsure to make contact with them regarding my ADT account, I sent an e-mail to ADT again informing them to get my name removed from this listing, no response was received from ADT like the previous time they never bothered to respond, I want this issue resolved ASAP, ADT needs to get their facts straight!!!!