"Overdue account" of a settled account

I app**** for a game credit card store card in November 2019. I took goods on credit and settled the account in December 2019. I then called after settlement to close the account and I was advisedby the consultant to keep it open and that I will not incur any fees as long as the balance is on R0. In January an amount R63 was deducted as a debit order, I called to enquire about that debit order and I was told that it was a mistake and that it will be fixed. Recently I received a message of an overdue account, I am also in the process of applying for a home loan so I was told that I have an outstanding account. I just called again this morning to enquire about this "outstanding amount" and was told that it will be resolved. I don't believe anything anymore and this has affected my credit score negatively.