Unauthorised debit orders

Hi I had an On Air contract for my dstv explorer which started 2 years ago. The final installment was paid in June 2022 and I confirmed via email that that was the last debit order. This week I get a call from On Air and before they could say anything I said I'm not interested. The lady said ok bye. Today i see an amount debited of my account for R79 and a new debit order set up. Old posts show that this is not the first time On Air has debited accounts without authorisation.