OK, so here's my take on this:
When he violates your boundaries, he shows that he doesn't respect you.
Don't get angry, think. What does that mean?
It sounds to me like he knows you're pretty much done -- and that he's trying to keep a "hook" in you by staying in touch with the kids. I think reaffirming your boundary like you did is a good thing. But I also think blocking his number would be a good thing.