Poor service - have not cancelled our debit order for months!

We are based in Wilderness near George. We previously made use of National Security as our home security service for many years, however they were bought out by Fidelity ADT quite some time ago and we went with the move. That said, their service started slipping, their response time was drastically reduced and sometimes they would not call at all when there was an alarm activation, and sometimes their security personal would arrive on the scene very late. After a year of poor service we moved to another local security company and are much happier, however ADT are still deducting our monthly security fees and they have not stopped the debit order. As it stands now, they owe us over R3000 in refunds but we cannot get them to acknowledge this error let alone refund us! It seems like they have poor service across their company from the security details, to the telephone operators, to the accounts department!