"She told me that she couldn't have me there because I threatened to cut my ex's head off, leave it on the doorstep, ring the bell, when her children answered the door, I was going to say Happy Birthday."
Holy wackdoodle, Amy! I'm sorry to hear that you had to live through *that* conversation! Yes, I think not answering the phone for a while would be called for in this situation, and I'm just so sorry for the pain that this must cause and has caused you over the years with this particular daughter.