sale of real prop. in installment, subsequestly sold to another.

I am a balikbayan who worked in singapore. Before i left 2 years ago, i purchased a parcel of land from "X" payable in equal installments for 3 years. We agreed that X will not transder the title to the property until after payment of the entire price. I paid the down payment and begun paying the monthly installments on the property by bank remittance from singapore. without knowledge and only after paying 25 monthly installments, X sold the property too Y. Y paid the price in full and had the title of the property transferred to his name. I don't know if Y had knowledge of the contract between Me and X.

Problem: I can no longer locate X.

Please advise me on what actions should I take.