Be very clear and concise about the cancellation of your DSTV contract.
Remember, if you read the contract that you signed, the onus is up to you to cancel the contract.
Multichoice can happliy assume that you still want the contract to continue forever, and have worded it such that they don't even have to provide the service, but will still charge you for every month that you have not told them you have cancelled.
Now, stop dilly-dallying about and phone Multichoice and inform them that you are canceling your contract. Then phone them the next day to confirm that the contract is in fact canceled, and then on last day of the month again, because somehow their debit order system has the power to automatically renew contracts.