First off, I'm really sorry your son is behaving so badly, I know YOU had hopes for him to return home as a different boy.
Secondly, I think as parents, we project our own feelings, wants and needs onto our difficult child's especially. We want sooooo badly for them to succeed, that our hearts get very wrapped up in them and we begin to think THEY want to live as law abiding, responsible citizens as much as we want them too. Sometimes it just isn't so. Your son is a manipulator. My difficult child was a huge one too. Maybe I'm cruel, but I finally had to take the stance of "show me the money" with my difficult child. I didn't believe one thing she said and I did block my emotions, because those emotions were MINE and did not reflect her AT ALL. My relationship with her had to become "business" only. It pretty much still is.
I think you were right to call the P.O. It should not matter one iota to any parent if you would get in trouble if you didn't call. If you are required to notify a violation, then it should be done, no matter what will happen.If your difficult child broke the rules, his consequence should be swift and harsh! What nerve to break the rules so early! What nerve to speak disrespectfully towards you! What nerve to threaten you! What nerve to bring violence into your home! Any punishment your difficult child gets is exactly what his behaviors / choices have earned him.
I personally would insist that the P.O. get him put back into Department of Juvenile Justice. It's very obvious to me that this wasn't just a little flub up. He needs a strong message that his behavior cannot continue.
Had I been you, I would not have shared with your son that you called his P.O. Mostly to avoid the response you did get, and then the element of surprise can be a very valuable tool. Sometimes we talk too much to our difficult child's and they figure out how to "play" our heartstrings better.
And since you asked (I know you didn't!) It doesn't sound to me from what I have read from you that your son has a mental illness. All bad bahavior is not the result of mental illness. He is a determined little buggar that hasn't learned that HE DOES NOT RUN HIS OWN LIFE, and HE CANNOT BULLY HIS WAY THRU LIFE, and THAT HE IS TOTALLY RESPONSIBLE FOR EVERYTHING HE THINKS, SPEAKS, AND DOES. HE CAN CONTROL HIMSELF and it is high time he learn that.
I have a lot of compassion for you right now, it's a terrible spot to be in. Take a breather when you can.