Hyundai Santro Gls — Reluctant to keep their promise on special discount

Hi,
I have purchased a car, Santro GLS from Trident Hyundai, Shimoga in the month of October-2007. They have promised me through email that they are going to give me special discount of Rs. 4000.00 meant for teachers. But till today even after repeated requests nothing has been materialised. I am thinking of filing a suit against them.The person who promised this never responded to my repeated emails and telephones.