I mentioned filing with Ebay because the seller stated in their listing that they accepted returns. Ebay should hold them to that. A seller that accepts returns can't pick and choose the reasons. They accept returns for any reason. IMO it is PP that seems to require letters from third party authenticators.
I see in the listing the seller stated "no returns coz all items I sell are genuine and precisely shown in listing pictures."
The seller has changed the return policy after you saw the listing?
Just by the photographs, I agree, the bag is fake.
OP, you might not be getting good reply from the seller because of her return policy. But I believe you should be able to win the claim if you takes all necessary steps one by one.
Good Luck!