Myntra.com — Regarding exchange of shoe for smaller size.

I have raised many issues regarding the exchange of my white shoe for smaller size... The delivery boy put the exchange on hold saying used product. But I dint used the product even for 1min. There is no marks or nothing on the shoes. They are new. I need an exchange from Myntra for smaller size. Myntra please respond on this issue. I am complaining about the same thing from 7th sep. I request you to send a delivery boy for exchange the shoes for smaller size. Myntra order I'd is 121319281644252899803.
I always had very worst experience with Myntra. I need an exchange for smaller size. That's it. They r brand new. I just need exchange for smaller size from the delivery boy. Try to understand what I am saying.
Thank you.