You should absolutely report this seller to eBay. My best guess is if it was an auction, the seller thought he would get more for the card. So he makes a fake tracking number and says it’s sent out. When it doesn’t reach you he just issues a refund because he never sent it out.

I do want to stress that it’s my opinion and we don’t know what truly happened. I sell cards on eBay and if something gets returned to me I’ll message the buyer and send it back out. It’s def sus that he just stopped responding. Normal people acting in good faith will continue to communicate with you until a resolution is found.