Land issues.

i had made an agreement to sell a land of 2400 sq of 12lakhs with in stipulated 3 months. The party paid 1 lakhs amount in advance. Later on, after 3 months he unable to pay any sum of money. Subsequently the party informed to give some more time. and I agreed, I waited for 2 months. Still yet himself unable to pay the balance of the amount. And I had sold the land to other party. Right away the 1st party asking for advanced money. which is I forfeited. He is now threatening me, that he will drag me into court and he will know how to retrieve money. . Can it really be possible? In any contract time is essence for contract. expert opinion needed.And can I file mental harassment case against him.