What legal actions can I take after the property complaint?

I made an agreement with a party to sell my property at an agreed price. He said he would buy it within a month, but he prepared an agreement for three months. When the time came to buy, he ignored me and switched off his phone. After two months, I found another buyer, and since the agreement was about to expire in 15 days, I sold my property to that buyer. Now, after nearly 8 months, the person has come out of nowhere and filed a complaint against me.