First of all go to Reliance Insurance Office and give complain in writing mentioning all the details and name of the agent etc.
But this as looks like is a fraud case so Insurance company do very little in it.But at least you can catch the fraud agent and stop him for doing it further with others.
Everybody please try to understand nobody reduce premium from there pocket so be alert and try price comparision sites before buying any insurance product from agents. Sometimes they don't know what coverage they are reducing. Better safe than sorry!