Is that the best your phone company has to offer, having his calls go to voice mail?
I would give them a call and see if they have any solutions for blocking him properly.
I don't know about PTSD but stress you do have! Every time you see that vm light flashing or hear that sound, you are getting a jolt of adrenaline? Or you are hardened to that now and just get a feeling of blah, I have to deal with this again. Whatever you're feeling it's not positive and that's not good for you!
I know this feeling, it sucks. This intermediate contact from him is allowing your stress about it to linger and be reinforced, there is nothing good about that. I hope you will call your phone provider and inquire about better blocking and barring that is there any way you can change your number? Yes, horribly inconvenient but so worth it for your peace of mind.
If you are going to go to the police is he threatening you in some way. I'm sorry I've forgotten if you mentioned it. Also, have you been clear in saying don't contact me. I'm just thinking, if all else fails, you may have grounds for a restraining order.