Flipkart — Cannot return a product because delivery person didn't mark as delivered.

Address:

Hyderabad

I have placed order for a NIKE shoes on flipkart, it was a open box delivery. When the agent came on 18th May, I was not at home, so he called me and got the otp. I gave the otp and when I reached home I saw box was there without the outer packaging which contains shipping and invoice details. The size for the shoes is incorrect, so I wanted to return them. Turns out you need the outer packaging to return or exchange the product since the delivery guy didn't mark the product as delivered.
I am stuck with 3558 Rs. with a shoe pair that is not usable for me.
Calling flipkart 1000s of times, the only thing they say is it has been escalated someone will get in touch, and every time I get a call it is for asking Invoice Number/Shipping details which I do not have!!!
I am so frustrated that I want to never order from Flipkart again. I and my husband also have worked in ecommerce companies as engineers. We know that if they want they can resolve it but they choose not to.