Property

Hi, my father sold a property on the basis of agreement to a person(2 people A&B partnership). But the person to whom we sold(A) couldnt give us the full money he agreed to pay and he payed only 50% of the total money. But the same person A, took money from two to three people showing that agreement and told them he will give the land to them once he pays total money. But now that person A is in loss and he couldnt pay the money even after 2+ years. So we sold the land to Person B who was the partner of person A, because he too had invested some money on that land. But now Person A is planning to send a lawyer notice to us questioning the sale of land to person B. We dont have the agreement copy too. We didnt cheat anyone. Please help us. Is there any solution to this problem??