Got cheated by giving money for interest to my father's son-in-law.

My father has given 15lakhs to his frnds son in law,He cheated my father,my father blindly trusted that guy,even he didn't take any agreements or notes.Now he was not lifting the phone.we have one call recording of that person,saying that he will return ammount when he gets job.we have completely loss our money.I doubt is that my father's friend is involved in this matter,but we don't have any proofs.please tell me, which way we can recover that money from that guy.My father did a mistake by expecting high interest on that money. And also please tell me legal way that how can common man can tap the phone conversation of that cheated persons. Thanking you sir/madam