Check your smart phone's brand app store for a call blocking app.
There are tons for every type and brand of smart phone.
Also check your cell phone provide to see if they have a block list you can add a phone number too, so you will never even get a ring.
You could also add the annoying caller number to your contact list and set the ringtone or action for that contact to be silent or ignore.
called my cell and then my work number. did not leave a message on either phone. If I don't know who you are I will not answer, and if you don't leave a message I will not call you back.
called in the early morning, and when i answered there was know one responding. said hello a couple of times and no response. this number has been calling often with same results or no message.