There are applications to block international calls but that only helps if the number is not spoofed. People that have SS7 lines into the telco system can spoof as just about any number. I wanted to kill those circuits but my employer at the time said, "they are paying their bills, arent they?". This was in the 90's. I guess the laws are every so slowly starting to catch up.
It should be illegal for Telco to allow SS7 spoofing for numbers that customer does not show they own.
Initial SIP setup shows number not to be a number they own, drop the SIP dial and be done with it.
Also, all US based phone numbers should have US based person tied to it. If they misbehave, drop them and blacklist them.
All this is solvable if we don't let phone providers get away with "Welp, the checks cleared, this is not our problem."