Wait until you can confirm the package status.

If it shows delivered (not refused or anything like that), contact the buyer as per eBay's advice, tell them that you have now confirmed the package was delivered to them and that you're issuing an invoice directly, and payment is expected within X timeframe.

Then contact eBay, advise you have followed their advice, and that you'll pay your "debt" when they buyer pays theirs.  (Since you said you have blocked eBay from accessing your account, I presume the refund was funded by eBay?). 

In all seriousness, I would actually take an approach that's something like this, assuming I was 100% unwilling to take on the loss, but actually wanted to continue selling on eBay, as they'll de-register your account eventually for non-payment of the outstanding balance unless you can come to a resolution with them.

You can try to argue that the buyer's debt would be to eBay, as you can clearly show you fulfilled your obligation as a seller, and the refund was at eBay's discretion, therefore you have no liability for the debt.