Section 420/406 and section 138

Dear Sir, I have given money to one RTO agent for registration of vehical about 40 thousands in cash and 5 thousand in his account. After that he said my registration will be done in a week, from that day till now it's been a five months and still he has not done my registration work, he has given in written on blank paper that he has taken money for registration and still work is not completed. I went to police station to file a complaint against him, police has traced that man and brought him to police station, he agreed that he has taken money and given his statement to police. He asked police to give him some time to give back my money, and he has given me a blank Check of his account as a security that he will give my money and take back his check. On next day he asked another weeks time to arrange money as he putting his father's house on some lender and taking money on interest, and he has written a statement on 50rs stamp paper that he has taken money for registration and not done, and used money on his own benefit. He agrees to pay money on 23may 2018. If not than I can file a case against him. On 23 Rd he ran away and not present in front of police. I think police is giving him support, now what should I do, can I file a complaint against him under section 420/406 or I should go for section 138 negotiable instrument act, what will be the best for me please do guide me. Thank You Nandkishor Yadav.