Where can i address my complaint letter to the President of Mitsubishi Motors, Phils?

My car is 2yrs, 4months old and I encountered serious problem on its trnsmission.I brought to Amcar, Phils but its still there for about 2weeks now. And they cant still ure when can i get my car back! I want to write a formal letter of complaint to the President of Mitsubishi motors. My car is a Montero Sports.