Hello. Thank you for coming to JustAnswer. I am Thoreau and I am sending this answer to you only a few minutes after you asked your question.
I am very sorry to hear about your son's situation. It's unfortunate that, after a break up, some individuals cannot maintain their composure and I'm sorry that he's been having to deal with his ex's behavior.
If the behavior continues, he could seek a protective order that limits her contact substantially. Further, her behavior could affect the outcome of custody or visitation
matters, as harassment and stalking can weigh against a parent in a child custody
issue. The judge in such a matter could also order her to keep him informed and to communicate using certain methods if doing so would better facilitate his relationship with his child. The conduct may also be criminal in nature and he could report it to law enforcement. At this stage, your son wants to take this matter to his attorney so that his attorney can send a letter demanding that the improper conduct cease. That may be effective at resolving the matter but, if it's not, his attorney can assist with seeking a protective order and petitioning to modify custody/visitation if he deems the situation may merit it.
Please remember that my job here is to provide accurate information about the law. Providing bad news is the hardest part of doing my job but it's a big part of doing my job well. If you feel that the law is wrong or unfair, I'd strongly encourage you to contact your legislators, as they are the only ones who can change it.