Myntra.com — Product Missing in the Order

I have received an incomplete shipment in the order ([protected])delivered to me and Myntra is resolving the complaint saying they did quality checks before shipping.
The original prepaid order was duplicated by Myntra and they shipped two different orders in same box (1 Original prepaid order and other duplicated order as COD) and I could not decline the COD order as both orders were in same box, on opening the Box i found only 3 articles instead of 4 and Myntra is not agreeing to refund me for the missing item.

First they force the customer to pay more by duplicating the order and now not even refunding for the missing item.