MTN and Mondo Contract Cancelation

I cancelled my contract before the cooling off period ended. I was still debited for the first month. I called them and they confirmed that the contract was cancelled and I was debited by error. They said I must call Mondo to reverse the debit order. Mondo said I must return it from my banking app. Now I have received another bill with the returned debit order from last month and a cancellation fee of over R1200.

When I call them they pass me from pillar to post. The next thing they will be ruining my credit record with this nonsense. If this does not get resolved I have to take it further.