someone is threatening to call the fraud deptartment on me.

i sold a car dealer a car to get rid of it. i told him it had an accident and he went over it and pulled up the history on the car and it came up blank. no leins or accident. now after 2 months he's calling me and telling me there was $16 000 damage on it and he wants me to give him back the money or else he's calling the fraud squad. i paid $3500 to get the car fixed and have the receipt and i don't know what he's talking about with his $16 000, what should i do?