Adt Security
Refund due

I recently moved to a new house in September, in which I sent a cancellation letter to ADT to cancel my service beginning of August, but at the end of August the payment of R350 was still deducted.
I have called the call centre and accounts departments almost every week since August to claim my money back and they promised to reimburse me every week but to no avail. This is very frustrating because I'm fed up calling every week to get money back which was never supposed to be deducted in the first place.
Please tell me how to go about getting my money back.