CAR TRADED IN NOT SETTLED IN FULL

I BOUGHT A CAR FROM THIS DEALERSHIP AND TRADED IN MY OLD CAR. THE DEAL WAS MADE SO THAT MY OLD CAR WILL BE SETTLED IN FULL. THIS DID NOT HAPPEN. THEY REQUESTED A SETTLEMENT EXCLUDING ONE MONTHS INSTALLMENT WITHOUT INFORMING ME. I ASKED THAT THE OLD ACC BE SETTLED IN FULL AND BELIEVED IT WAS. THIS DEAL WAS DONE WHILE I AM WORKING IN NIGERIA SO I TRUSTED THEM. I WAS CALLED BY THE BANK YESTERDAY ABOUT THREE MONTHS AFTER THE DEAL TO INFORM ME I WAS OWING THEM MONEY ON THE OLD CAR. I ENQUIRED ABOUT THIS BEFORE AND WAS TOLD IT WILL BE DELT WITH. IT NEVER WAS. NOW I AM GIVING THE RUN AROUND AND THEY HOLD ME TO THE SETTLEMENT THAT WAS AQUIRED BY THEM, WHICH I NEVER SAW. I WAS TOLD BY THE SALESMAN THAT THE ACCOUNT WAS SETTLED. THIS MORNING A VERY ARROGANT DP CALLED ME WITH NO SOLUTIONS. I AM VERY DISAPPOINTED IN THIS PEOPLE.