This number calls all the time. And is really annoying half the time they hang up and when you do get to some one and you ask who they are they just hang up so everyone try to block this number.

Unlisted in phone book and always calls and no voicemail

Most likely CDI Affiliated Services, Inc of Nampa, Boise and Pocatello, Idaho.  "Specializing" in medical bill collections.

Calls and when I answer they hang up. Never leaves a message and when I ask who's calling they hang up!

This number will not stop calling me. When you answer there is a brief silence, then they hang up. If you don't answer it they leave no voice mail but turn around and call one more time. . Absolutely ANNOYING.