sell faulty product and don’t return it

sir i have buy a product 10400 mah MI powerbank from bookmyoffer.com on 26-04-2016 my order number is 80467750732031 and it delivered on 28-04-2016 and it is faulty product it not working and i have to complaint this is on bookmyoffer but don’t get any response and its product price is Rs 450 .please sir take it very serious and do something .thank you