Trying to cancel account

I’ve been trying to cancel my contract with telkom since May and we are in September, they have been telling me it’s cancelled and then I keep receiving invoices and they have been debiting of my account for free me deals after I asked for the sim to be pay as you go, as I’m not using the sim at all, as my phone was stollen, how do I get refunded for the debit orders and get it stopped.