Myntra.com — myntra delivered wrong size of the product, denying to take it back

I had ordered an 'M' size underwear, but Myntra has delivered an 'S' size underwear. Now despite of complaining many times to their customer care, the executives are saying that they delivered the right product.
I have already sent them the product image where it's clearly written as 'S'.
Not sure what to do, probably not going to order anything from Myntra anymore.

My order ID:[protected]-2844603
product code: PZRM00100-R6

After the complaint, they sent the below mail:

"This email is regarding your complaint against the wrong product delivered for the product "Park Avenue Men Red Solid Briefs PZRM00100-R6". Please accept my sincere apologies for the inconvenience caused to you.

Post reviewing your case we have found that we sent a correct product to your end. Hence, your claim has been declined. Moreover, we are unable to serve you further on the same."