This number calls every day and never leaves a message. Won't answer because do not recognize number.

Try not allowing them access to leave messages and see if the calls don't stop. No type of answer, time to move along eventually. For the majority of telepests, little can be accomplished by them leaving messages. Outside of maybe finding out your ID and your number works, you can't cheat an answering device.

Calls once a month and doesn't leave a message.

Real problem, calls daily and hangs up! spammer or nuisance caller,

Sounds like you're answering the calls, and in that case, expect them to continue. They call who answers or numbers that have a reputation as often having one of some kind. No kind of answer eventually means irritation for pests.