Cell C blacklisted my name but I have paid

Hi I had a two years contract with Cell C from 2019 to 2021. It was a phone contract. We had an agreement that they will debit from my account so after looting it happened that they could not debit because of technical problems they say. My account from then was on errors because I realized after two months that the money was not debited. I paid the money myself to the Nedbank account that they gave me. October last year I paid the balance of R710 and my account was paid up but I didn't get the paid up letter.. They even open my line and put my number to be prepaid.. This January they attorneys called me saying that I'm in errors with Cell C. I have sent them proof of payment but my problem is not yet solved.. Their attorney have already blacklisted my name. Can Hello Peter help me solve this problem please..