If you're getting repetitive unwanted calls on a cell phone, your service provider (Verizon, AT&T, Sprint, etc.) has a feature that allows you to block a specific number, so that you never know they're calling no matter how many times they try. With Verizon, it only lasts 90 days, but you can renew it if 90 days doesn't discourage the caller. Great stuff. And, it doesn't cost anything. Even better!
Now, we just need an unwanted poster block feature.