Adidas — A missing item in my order

I ordered some products on adidas on 13th may and i received it on 17th may. A item was missing in my order but i already gave the money, adidas is neither delivering the product nor giving the money back. After 15 days of so many phone calls in which so many of them were not answered and mails after mails, they are saying that they dispatched the product and they can't do anything in this.
I am literally feeling mentally harassed. It's their fault, they should give my money back. The product cost me 1440 rupees.