Telkom Cancelled Contract - Account/Debit order nightmare

I cancelled my contract in February 2021. I continued using the sim card for SMS only, communicating with one person only, so Telkom used to charge me around R100 or so. I stopped using the SMS feature in July when the person I was using it for got a proper phone with Whatsapp/Telegram. But Telkom continued to charge me the R100. I paid end of July, August while trying to contact them, to no avail. End of September I reversed and disputed the debit order. Yesterday I got a notification that says I owe R402.70 (R302.70 current and R100 arrears). If they have been charging me R100 where does the R300 come from now! What must I do for Telkom to leave me alone??? I regret the day I took a contract with them,