Vehicle finance , Can't get account closed

I am really frustrated at this point in time. I financed a vehicle in 2014 and settled the account in Nov 2019 without skipping a payment ( the final amount was around R3700). The settlement quote was provided from the banking app and I made a payment and the account was closed. A few weeks later a received a sms stating that I failed to pay my account and the account suddenly appeared on my banking profile as open and in arrears. Another debit order was deducted. I called standard bank and it was explained to me that they made a mistake and they never closed the account properly, whatever that might mean. The account was closed and I received a paid up letter together with The Natis document of the vehicle. In Jan 2020 I received a refund. Fast forward to Jul 2020 and I received a demand of R18k from Lawyers. I provided the info I had to them and they returned the account back to Standard bank. I phoned Standard bank and another service request was logged. Request was closed and I have not received feedback yet. I will advise anyone to rather finance a vehicle elsewhere as after managing the account flawlessly for the full term , you get treated like this. This is negatively affecting my credit status as Standard bank reports this as an arrears account. How is it possible that it is so impossible to get this resolved?