ebay issue, what would you do?

[brewing]

I sold a card on ebay on August 9th. Tracking shows out for delivery on August 14, but never scanned as delivered. I have had similar situations and buyers left positive feedback indicating delivery.

First time I heard of issue was on Sept 2nd when buyer opens a case.
I've gone thru steps with USPS, still open with them.
Buyer requests to close case and ebay decides in their favor on Sept 11th. Without delivery confirmation I don't believe I'll be successful in an appeal.

Buyer has been unresponsive to all messages sent outside of his ebay case.
Checked today and the card is in his PSA T206 registered set. He's not a member here, but is on blowout cards.

It's a $70 transaction.

It's possible he added it after purchase, but I think he received it and has scammed me. Mostly because he has completely ignored every message I sent to him outside the ebay case system.

Do I out him on Blowout Cards?
Do I ignore it and accept the theft?
Any other thoughts?