paying for cars that is cancelled

We sold two cars in August 2023, and cancelled via email. The cancellations department acknowledged this via email on 1st sep. We than had our last car in a car accident that was written off in October and cancelled this car. This was never done on the system. Have logged tickets, done 9x phone calls and we are now being threatened to be handed over and our credit rating affected. I speak weekly to your consultants, and than we get another sms saying account in arrears. I am done with this. If I do not get it sorted out by Wednesday the 7th of February 2024 I will be going to the ombudsman......