Failure to cancel contract properly

My pensioner grandmother had a month to month contract with Telkom for data. This was cancelled in January. Ever since then every month there has been debit orders going off that has to be returned and not even amounts that the contract was for (which has a fee linked to it for every single one returned). So not only are you causing her additional costs monthly you fail to cancel a month to month properly. Pathetic service. Really hope no one falls on the trap of signing for any type on contract. All evidence are at hand that it has been stopped and still THE SAME ISSUE MONTHLY!!!!