Total incompetency

I was a client with MTN for more than 20 years. In December 2020 I decided to cancel and close my contract with them. On 14 December I phoned and speak to Thelma, asking what the procedure was to cancel and close my account. She said the outstanding amount of R399+ Vat = R458.85 must be paid, then the account will be closed - this is all that is outstanding, she gave me a Ref no of ***. I paid that amount of R458.85 on 14 December and thought my account was closed. Then on 16 Feb I received an email with 2 documents, the Tax Invoice says I owe R0.00, but the statement says that I owe R752.97. The R399, which I paid, is on this statement - and there is no indication of the payment I made. I tried phoning - but 083135 from a Telkom line doesn't work. I send messages via Facebook, I mailed MTN several times with all the info - but still there is no feedback or answer to this issue. What must I do to get this resolved and closed ?????