Why do you answer it ?
Get the Police involved then. Show them the text messages and have him charged with harassment.
Great point Stephanie ! Do not give this guy any attention what so ever, and certainly do not allow him to know that he is bothering you. That will just make his crazed mind do it more.
A two word reply comes to mind. It's something like "Fu(k off" !
I don't know what kind of phone you have, but on mine, I have a block feature. I love it. It is the best feature on my phone.
On my phone, I go to the number that I want to block, and go to options, and down near the bottom of the list it says add to reject list. I can block up to 25 numbers.
Maybe they are upset with you.
passive-aggression? well, it is friday...