Telkom's overcharges

I have been happy with Telkom until a payment got returned after lockdown. I had taken extra data as there was a lot of communication going on obviously & thought there was enough in my account to cover it. It appears there was a slight shortfall, possibly to a bank charge that went through & it was returned. I paid it in cash a few days later when I discovered what had happened. The next month an amount of R202 was added to my payment which I queried telephonically, via e-mail and I went into the Telkom branch in Knysna who assured me that I would receive a phone call. No phone call came & also no e-mail so I returned the payment & paid the correct debit order amount in cash. The following month R404 was added to my payment! Telkom had charged me an extra R202 for returning their incorrect debit! I finally received an e-mail saying that the R202's were charges for returned debit orders! I returned it again & paid the correct debit order amount in cash. How can Telkom charge such a lot & keep on escalating it while the query was going on? Unbelievable! How do I sort this out!?