Debit orders going through without any request

I cancelled my dstv a year ago. A few weeks ago I noticed that the debit order went through for April although I did not request it. On enquiry I was informed that it was a “system error”. After a week I was refunded. However I noticed that the debit order also went through for March. Despite two phone calls to customer services I have not received any refund yet for the latter amount. The last call was more than a week ago. It is also strange that the two amounts differed and it also differs from the amount I used to pay. The 3 calls I made to customer care were all longer than 30 minutes and for my own my cost. Very unhelpful service.