Welcome to this family where you will find comfort, strength and support. No one has all the answers but by listening to our struggles and how we may have tried to manage them, you might find the right path to your own recovery.
I too struggled with this similar problem with my 30 yr. old son. When he didn't get $ from me anymore he became very vicious. He keyed my brand new car to the tune of $2,000.00
and sent messages that became physically threatening. He even used my work e-mail. To a large degree for a long time I allowed the texts, calls and e-mails. Somehow in my warped sick thinking (and kind of compulsive thought process too) I felt I had to keep listening and reading all the hurtful things he'd say. Like it was a punishment to myself for not being able to save him. Also, I kept listening, hoping that he was calling to apologize and say he'd changed. This has not yet happened and I didn't realize it's going to be a long process for him when and if he does. So no time soon.
Some people can rip the band-aid off fast but for me it was baby steps. First I put his e-mails into my deleted folder (but I kept going there to look for them anyways), I'd block his texts but not thru my cell phone provider so he'd still be able to leave voicemails. As Copa mentioned, it's our "FOG" (fear, obligation and guilt) that keep us in the loop. It took therapy, this forum and Al anon to help me get strong enough. Eventually I was able to stop all these avenues of communication and that's when little by little my anxiety subsided. It's not gone altogether and in fact when I'm ready for bed, I now put my phone on "silent". I have another son with issues too, who is not blocked and could call at any time. This is such a trigger for me.
You, however sound like you're ready to "rip the band-aid off". If you truly are, you will be able to work this through. As someone else mentioned, don't pick up a call that you don't recognize the number of but do save your texts or voicemails should you "need" them with the police. When you need to "silence" your phone and enjoy some "calm", do so. Take small increments of time to find peace. Eventually, you will grow to want more of that and will do whatever works for you to attain it.
Also, no replies back. No need to rebut what he says. It only adds fuel to the fire. They know when they've got you engaged, even if you're defending yourself or trying to defend family members who he's involving, he's still winning. It gives them ammunition. As time goes on, the calls may subside. Be careful, however, and be alert to your surroundings. Even if he is out of state right now. They are not happy when we make changes for ourselves.
Be safe, be strong!