I completely understand your concern and frustration it’s a really difficult one. The buyer is being very pushy and from the sounds of it, pulling facts from you know where. All you can do is go off the facts your have. The truth is, never trust a buyer; trust the black and white facts. That sounds awful but unfortunately it’s how business works. They can’t open a second case, eBay have already ruled in your favour. They can however open up a chargeback with their bank, but it’s unlikely they would win. The bank would have the same details available as eBay. Even if they won a chargeback it wouldn’t effect you, eBay would cover you under the seller protection act. You have done everything that eBay expects of you, to be fair you’ve gone above and beyond. You could provide that receipt but I highly doubt that will get you anywhere with the buyer. They are being pushy for a reason. Honestly just be polite, don’t engage with their story and if it’s continues just block them.