Defrauded by 2 wheeler buyer in Bangalore

I have recently sold my 2 wheeler in Bangalore. i found a buyer online via OLX and agreed on a selling price of 54000. The bike ownership transfer was done via an agent from the local RTO office in Ramamurthy Nagar in Bangalore. The buyer payed me 48000 via cash and online transfer and he promised to pay the remaining amount by (Feb 02, 2019). I am not in Bangalore anymore as I shifted to Rajasthan and I am fed up of following up with the buyer to pay the remaining amount. He has been postponing it every single day and I feel i have been throughly cheated. Please give me some way so that I can get the money from this fraud buyer. Please note that I can not make the journey to Bangalore to collect the balance amount. (Note: Before handing over the keys I made him write the entire paid and balance amount on a piece of paper and it is signed by both of us. He has a copy and i have a copy as well)