What action can i take if iam forced to enter into a sale agreement

Hello, I am searching for a legal solution as the car owner forced me (purchaser) to enter into a sale agreement on a 50 Rs. non judicial stamp paper,against my will, instead of getting paid for the damages that i'd done to his vehicle. The agreement was executed at his residence and not in any public office. Also, the sole witness is ready to give the statement that the agreement was made to sign forcibly. Is it enforceable in the court of law, if it is not duly notarised/ registered ?? If yes, what could be my options to tackle the above said situation.