Theft case and FIR can be filed if taken someone's left item unattende

Dear Sir, I was travelling from Blore to Kolkata, i was in hurry and by mistake i had taken someone else hand bag. After 15 days Blore police called me by seeing CCTV footage of Airport and asked me to return the bag. After i got the call i went to Blore to return the bag with all the belongings and met that person who is the owner of the bag.Now that person is giving threat that he will do FIR against me if i do not pay 1.5 Lakhs to him. Also he is saying he will inform at my work place to spoil my future. I got frightened and paid him 1.5 Lakhs by fund transfer to his account, and finally he agreed and given written statement in ploice station that he dont have any complaint against me. I have given the same statement into the police station. Can he do any FIR? Now my question is whatever he has done by forcing, threatening, blackmailing is that not an offense by law? If yes what action can be taken against him and can i get my money back from him. Please guide. Thanks, Roy