Myntra.com — myntra account has been hacked

My myntra account has been hacked by someone who is from Delhi. Hacker used my myntra gift credit of 2000₹ and bought one fit it kind of band.I got to know when I had received few OTP for my order and when I logged in I saw the order is placed already. I canceled it right away and changed my password.
From my account address And I found one new address and Mobile number is been used for the order. When I called him, the guy one the other side said I'm a hacker I hacked your account, Complain to anyone if you want and do whatever you can. He was so rude.

The main question how would he know I have myntra credit. Because hacking a normal user is no use. I suspect there is some problem with Myntra as well

Hacker address and mobile number.
Malkeet,
Agrawal sweets Near reliance fresh,
Kokrala,
West Delhi,
Delhi.
Mobile :[protected]