Peter here from Shopify Support!
While you wouldn't be able to block specific cards through the payment processor you could look into using a free app called "Fraud Filter". You can use this app to create a variety of rules which can automatically cancel and refund orders if they come from specific regions. We have some further documentation on this app here if you need it!
If there's anything else I can help with please don't hesitate to reply back and I'll happily help out!
All the best,