Cell C account mess up

I had a cellphone contract with Cell C which i opened in 2019 and i paid the full value in March 2020. They deducted their last amount outstanding of R70 after doing their reconciliation in April 2020. Last month I checked my credit score report and found that I still have a balance of R70 as an outstanding value on my account. I then compiled my bank statements and sent all the proof to cell c because i needed them to update credit bureau and remove their account under my name as it is fully paid and it is messing up my scoring. I have called and emailed and no one has assisted. I am tired of Cell C as I have done nothing wrong and I need them to take this seriously.