not attending the complaint and sitting silent on my complaint

Location/place: House No.924/1 gali no.8 gobind puri Kalkaji. New Delhi:110019

Name of company/service: Hitachie

I purchased a month back a A/c. from the said company and very first day i found the product is not ok and i lodged a complain but no responce five times i lodged a complaint to the office but they send a mechanic why should i accept a defective piece from the first day i am contineouly lodging the complaint but no responce