Ya, I know how you feel.

First, you need a block function on your phone.

How mine works is, it's a call display phone, and if a number comes up, like sales people , then I program that number into my phone, put on the block function, a viola!

Now, if you don't have the block function on your phone, go buy one, as I'm not too sure how else to block people. Maybe phone up the phone company and ask them to put a block on that particular number you are wanting to block.