Called my cellphone a few hours. I ignored it and they - of course - did not leave a message. I searched the number online as I normally do and thanks to 800notes.com, I usually get useful information about these types of pain-in-the-a$$ callers.
If you have an Android phone I recommend SPC (Super Private Conversation) app to block these callers. Calls can be blocked on a number or area code (prefix) level. It is a very effective app and I believe it is offered as a free app and a PRO version (to remove ads).
Sorry, but peeps on iPhone do not have an option to block calls unless your phone is jailbroken.