Money missing on credit card

My husband and I have been making payments to our credit card. The payments show on the transactions as credits, as well as on the statement but do not show on the balance. We have been back and forth with the Nedbank customer service trying to figure this out and to our surprise they say they do not see these credits on their side. Question is, how are we able to see them but they can’t??? What system are they using. It’s soo frustrating because they keep charging us yet there’s money that’s supposed to be there but it’s not reflecting. We have gotten to a point where we do not know what to do. It’s very frustrating. We are being transferred from department to department.