worst service ever

We receiving the worst service from MFC we wrote off the car and we have tried to call them to confirm the balance to settle and how to settle but every time we call them we are told it's with a different department and were going to get a call back and nobody is calling us and the documents we received said they were going to deduct on the 25th august and nothing went off and the problem is next month they going to add interest and who is going to be required to pay that interest ? not us that's for sure cause it's not our fault and we have proof what a useless company