Frustrating Service

Account was settled in October and received settlement letter. I then started receiving emails from them that I’m in arrears on the account. I contacted them a number of times and they say they will look into it. Nothing is ever done as I have now started receiving messages from FNB themselves about the account being in arrears since October. It’s very frustrating as one is trying to pay off debt and work on credit record. But this account is giving me no joy because it appears as in arrears even though I have a paid up letter.