I am with springy 100%

I would open NPB dispute, close it in 4 days, and this idiot will get strike, you get your fvf back, and relist.

Add this person to your BBL now, don't wait.

Doubtful they know anything about eBay if they think they can force you into changing the terms of your listed item, and does not sound to me like they are the sort who will pay on your terms.

Once you close the dispute siting payment still not recevied - they can not leave you feedback, and iif they do, eBay will remove it with a simple call from you.