Buyer refusing to pay as per agreement what can be done

I, bought a vehicle in 2012, but failed to transfer it on my name. Few months back I handed over the vehicle to an Agent to further sale it. Two months later when the agent failed to find any deals, he decided to buy the vehicle for himself and verbally stated that he would pay within a period of 10-15 days. But before he could pay, the vehicle met with an accident. The vehicle was totally damaged. There was no insurance. I do have a agreement on a Rs100 stamp paper duly signed by the Agent and his Father. But they are not paying. its been 6 months, they haven't payed a single penny. Kindly assist me!!