Stolen gold item was mortgaged and now our money is stuck

My father is a professional money lender. He takes gold as collateral and give money to his clients in return with applied interest. A person(I will not disclose his name) staked his gold chain for 40,000 INR to my dad and agreed to pay the money back with interest in 2-3 months. Later, we found out that the gold chain was stolen and police seized the chain. Now, our 40,000 INR is stuck so is there any way to recover this amount? Is there any legal procedure to get back our money? That person actually stole that chain from his own relative(his uncle) and his uncle filed an FIR and that was when he was found to be the culprit. We also did ask him If the chain belongs to him and he told us that it's his own chain and when we asked for the bill of the chain he simply told us that the bill is lost and it is true as after when the police seized the chain we gave a visit to his uncle to clarify things and he really didn't have the bill.So, Is it possible to file an FIR without having the bill of the stolen item? How do we get back our money? Can we even get it back?