The seller was mortified. They claim they never canceled the card, and they will refund my money ASAP. The seller is trying to figure it out with Chase Visa.

Edited to add: it probably helped immensely that the seller also has an eBay storefront, so a negative feedback would've been a bad look. If it was some random person who uses eBay once a year, I probably wouldn't have gotten such a pleasant resolution.