Taking money from a Dead Person

my father died last year, 07 January 2017. He had a Cell-C contract, no device payment, just a subscription. My mother went into Cell-C and wanted to transfer the contract to her name, she gave them a certified copy of my father's death certificate (to prove he was actually dead). The branch then told her that they wanted to know where the money came from in her bank account, this is actually none of anyone's business, the money in her account is a regular payment every month. They then told her that she could not have the account transferred, she then asked for the contract to be cancelled. Every month Cell-C have been debiting my mother's bank account for my dead father's contract that isn't used. My parents were not married in community of property, she is therefore not liable for any of his accounts now that he is dead. The estate is also finalized, so he really is dead. Yet Cell-C still debit her account, and we keep returning the debit order. We now received a FINAL DEMAND, for my father to pay. I emailed the death certificate again, and yet another debit order goes off. I am more than willing to give Cell-C the GPS location of where his ashes are spread, to issue the legal notice. You are probably the most insensitive bunch of *********** people I have ever dealt with. Dealing with Cell-C is a nightmare. Now please can this be rectified and the debit orders stop from my pensioner mother's account.