Amazon - Refund not received

I order Boat headphones (order no - ***-*******-*******) which I returned on **st Jan; because the item looked kinda big on my head and also seeing the packaging it seemed like someone had already open it before. The delivery guy clearly inspected the headphones, asked me for the return reason to which I replied the same. He did some updating on his phone and left. Now, around *-*th feb I called saying that on the tracking page the item doesnt seem to move, like it has been stuck on the same place from the beginning and also there was an eroor coming that the 'item may have been lost in transit'. I got the reply that they have submitted the report and asked me to call again on *th feb for further updates. To my surprise on *th feb they said that THERE WILL BE NO REFUND because upon checking they found out that I filled the box with some junk and that the actual headphones were not there. I have been going back and forth since then and they are not helping ; just denying on my face.

I also work in Amazon US marketplace. The rules are so relaxed for them. People get 'Delivered Not Received' concessions even for more than $*** but to me even after returning the exact item I was called a fraud.

They also mentioned that since I have requested various returns and replacements in the past, they cant do anything about this order.
Its not a small amount for me...**** its too much to just let go away like this.

I am registering this to get my refund back or if not I am ready to accept the headphones back (if I have to carry that hefty bult over my heas) or just return that same exact box back which they are stating has 'junk' inside.