Tired of getting phone call.  How can I block this number?

Expecting a call to schedule something, I picked up to hear no one on the line.  It's my practice to never pick up so I can't be on any lists of people who pick up at a given time, and I would never "press 1" to not receive any calls because I hear it can open your line to the caller's use.

Have called 2 days in a row, during business hours, no voice mail left.

Calls 3 or 4 times a day; nobody there when I pick up; no message left when I am not. I call back and it says "this subscriber's voice mailbox is full."

Don't get it -- why does this continue to happen if they aren't going to say anything or ask me to buy anything?

I pick up ... they don't answer