Your husband is one of those "poking the bear" kind of people. I am pretty sure he is doing what he is doing to annoy you and its working.
NC is a request so he doesn't have to do it - I most likely would not block his phone when he had my child.
Perhaps having someone drop your son off will work for a while but its not a long term solution. At some point you will have to resume these drop offs.
I learned from a Master Ignorer that the best thing you can do IS ignore. No reaction whatsoever. No response whatsoever. You can't control him but you can control you. Maybe looking it from there perspective of why he is crossing your boundary will help you with this. He's a jerk and only doing what jerks do which is expand their jerkishness to higher levels. He is feeding off your reactions - I would try not to give him any more fuel. When people stop getting reactions its not fun to poke the bear.
Tough situation for sure. Sorry you are going through this.