These people are so annoying calling all the time.
When I get out of state calls I do not know I send them straight to  voice mail and of course they don't leave one. I started saving them as a contact called Spam with "Send to voicemail " option clicked. After a couple of times they stop calling on that number and choose a new one.  I don't have to listen to my phone ring.  After a couple of months I delete them.