Outstanding arrears (that area appearing all of a sudden that the car has been paid off)

My late dad (ID number ***, account reference number059736:071723)had a taxi that we were still paying wit SA taxi, it was repossessed but I managed to pay the required amount that was needed to release it. It was released with new financing plan and every month we paid the required amount. The last payment was on the 6/2/2023. Prior to that I received a call requesting that we pay arreas of R8730,which I did not undersrand where they were coming from. I spoke to consultant to try and find out as the arrears reflecting on my statement were -R4 969.87, the lady confirmed that the amount showing was the amount in advance hence it was showing a minus sign. Now that the car was settled last week I have received numerous missed calls and a message threatening that I should settle R8730 within 24 hours. I did raise this to the consultant that they must resolve their errors as we do not expect to get call now that the car is near to being paid off.