R1800 refund owed - been waiting 4 moths

I cancelled my ADT service and gave the requisite notice. The service was duly halted, but they continued to deduct the monthly payment for a further 3 months. As soon as I discovered this, I contacted their accounts department (21 Oct 2015). To date, despite many phone calls and hours on hold, and a number of emails, they have not yet given me a full refund.