Mobikwik — No longer valid cashback offer code lum300

Address:	Krishna, Andhra Pradesh, 521228
Website:	www.mobikwik.com

I purchesd a lumia 640 xl mobile. when i purchesd they gave me cash back offer of 300 per month upto 12 months. by seen that offer only i purchesd that mobile. this code worked for 3 moths. after that not applicable. it showing that this code is no longer available. what i hav to do.. i put a complaint to both mobikwik, microsot. microsoft web site also published about this offer. but they not giving any responce. what i have to do to get my cash back offer, other wise is there any chance to go to court for justice