Unhappy client

My contract with mtn ended on 2022 I was told to pay a certain amount to settle my contract I paid and I was given a reference to show I paid.to my surprise this year I was told by my bank that I owe R350 my account is handed over to lawyers I paid but still shows I am owing I went to mtn Mthatha plaza I asked to speak to manager I was told he is not in I asked to speak to supervisor i was told he is not in and they don't have his number at the bank I am told my account still shows that I am owing when I go to mtn I am told to call call center and their phone keep ringing with no pickup