Just block caller on your phone if you have that capability. iPhones can block.
Tap on the ' i ' inside the circle, to the right of the number, scroll to bottom, tap block caller. Simple.
As soon as you see a number that you don't recognize, don't answer, if it's someone that knows you, they'll leave a voicemail, if not, look on this site to see if others are getting called from that number and source it out. Block it. That's it.