This really is a tough call. I'm not sure there is a "right answer" that will fit every situation.
A few thoughts are running through my head on this... for example, what if BH had been in the hospital and was reaching out for help? I don't know if you have kids, but same thing, what if someone was hurt, or what if the kids needed to talk to both parents about something?
Like others said, it's possible that if it was an emergency, BH would follow up with a text or another call, but to be honest, from a BS perspective, when you call your WS and they don't answer, it can often feel as though "they don't care" or are ignoring you, or are even perhaps with their AP and don't want to answer your call. Get what I'm saying? Most BS's aren't too keen on giving multiple chances when they are feeling actively dismissed by their WS.
The other thought (my first reaction really) was simply that, since your BS requested the NC, they are also the ones to decide whether it needs to be broken or not. (You also have control over this, as you may also desire NC, but I am guessing that the NC is not really what YOU want at this time). Who knows why he called? Yes, it's possible that it was to cover something pleasant such as you doing the work, or maybe his feelings on something. But it also could have been to initiate a discussion about paying bills, changing jobs, initiating a divorce, asking for more details about the A, needing a favor, or needing you to sign something... What I'm saying is, HE requested the NC so if he's calling you, he's made the decision, for whatever reason, to break it for that moment. Not answering may feel, as noted above, as being ignored.
Part of me tries to put myself into the BS's shoes... what if I called my WS? And they didn't answer? Would my reaction be, "Good for them! I told them not to talk to me and so they refused my call. Good job WS!" Well, I have a hard time believing that's the way my brain would go. Is it possible they might think, "Oh, I guess they aren't near their phone, or are maybe busy doing something... no big deal, guess I'll call again later". That's possible. But if so, I suspect you'd have heard from him by now.
I wish I had some sort of advice for you. There is no good answer here. If you texted him and said, "Hey, you called, and I struggled with answering because you requested NC, but I also didn't want you to think I didn't care" that might help initiate a conversation, but it also may be seen as breaking NC. Not doing anything might be seen as you respecting NC, or it might be seen as you not caring - we just can't predict that.
Just to echo some of the others... your effort is showing. I too admire the fortitude you had in not picking up that phone for the sake of "doing the right thing" while not knowing the outcome(s). It's too bad we WS's didn't have that same fortitude when it came to saying "no" before. That's the part that makes our BS's want to bang their heads against the wall. But you are working on it now, and showing strength. That's good. You'll need it. Keep doing the work, because regardless of how your marriage turns out, you will still be you, and so that "you" should be the best you that you can be. Everything is hard right now. By doing the work, you plan to never experience this again.
