Flipkart — returning of moto g

i bought a moto g 16 gb phone through flipkart.com. they provided me with a defective item. as just after `1 week i was not able to switch on my phone. i charged the phone and waited so that it might work . but nothing happened. so next day i called their customer care and reported my matter. i raised a request for refund. but they are not taking any action on it. and everyday they a`re giving me lame excuses and telling me to wait for next 24 hours. tell me how can i legally take this issue against flipkart.