Cancellation of data simcard

I opened a contract simcard in MTN online in April 2021 so I didn't know that when contract ended you must call them on 135 to cancel until I noticed that they debited R938 in my account instead of R638...so I reverse the money same day I went to Blue route mall MTN branch to ask what's happening they told to call 135 to cancel the simcard I did call on 26th May to cancel the lady told me to pay an outstanding balance of R499 from the simcard which I did on the 27th and I destroyed the simcard on the 26th since they told these are the charges because simcard is still active and working ...when I called on the 28th to tell them that I have paid the money so they must cancel they said it's reflecting on their side ...I called them again on the 30th of May and they said it's cancelled until I saw another debit order of R938 from account again and reversed it ...can you please help me because it seems like they don't want to cancel this data simcard