My suggestion is to just ban specific regions or countries and you can cut 80% of this fraud.

I'm not going to name those countries outright but you should never ever be launching globally until you have these safeguards in place.

Once you are known to be vulnerable to a certain scheme, it quickly becomes known in that region/country.

Again and again I'm reminded why high trust societies remain high trust and why low trust societies rarely transform into high trust society.