Account had been settled in 2018 but stating an amount of R592 is still to be paid

Recently I have checked my credit score ,and I have noticed under accounts, there is a current balance for R592 under CELL C.This cellphone contract was settled in 2018, where a settlement statement was sent through and I had paid the full amount. I have even submitted through a proof of payment to stimulate the closing of the account .Therefore there seems to be a pending amount that needs to be paid .Clearly there seems to be an issue of communication here .This is a 2018 issue ,and it is now 2020.I will not be paying anything further to this account ,and would very much like this issue to be addressed and solved ASAP!!!