I think if you take this up with Amazon on their chat, and show them your evidence, they will refund you, no questions asked. They may send you a prepaid sticker to return the item to them free of charge, but I've heard of this kind of thing before. Amazon customer service are excellent. Contact them. I think they will make you happy.

And it won't matter that it's a third party seller. They will refund you from the seller's account. They can do that. I've heard of them do this before.

The other option is to write 'return to sender' on the package and hope it gets back, but that's more risky. In the UK, that's supposed to get the item returned, but only really when it's been unopened.