Amazon India — non acceptance of consignment received

Address:

Hyderabad, Andhra Pradesh, 791102

I had placed an order (Dell laptop) on amazon india on 30th june 2018. After received the item on 9th july 2018 it was found defective. On the same day i request for replacement but they told me that due to stock nil for replacement they will iniate for refund as well as the courier cost and i agreed. They instruct me the process of returned and i followed the instruction and returned the consignment via indian post courier number ee[protected]in on 10th july 2018. I track the consigment daily and it was found that the consignment was delivered to amazon seller services pvt ltd on 16th july 2018. But from 16th july 2018 to till date the amazon seller mailed me that they did not received the consignment yet and when they received the item they will refund my money with courier cost. The laptop cost rs.58704 and courier charged me rs.519. The amazon seller services pvt ltd is not accept that they received the item and delayed the refund. Kindly suggest the way how i can get back my money.
Thanking you
Toni sitang eko