DSTV Accounts Department don't do their job properly

I have had a debit order plan with Multichoice for some years now, and I changed banks in Feb. I gave through all my new details to them, and they have it on their system. Still they did not deduct my payment on the 1st of April, nor the 1st of May. I've had to phone them twice now, and stay on the phone for half an hour per time. They did not come to me from their side and said that I didn't pay or anything. No it's costing me even more in calls, because they did not do what they were supposed to do! The guy that I spoke to today, told me he was going to send an email to their accounts dept, and cc his superior as well, and ask them to phone me back. I really hope that they will phone me back! Because they also charged me interest, and I REFUSE to pay that! It was not my fault to begin with. I will have to wait and see if I get a call/response.