Ex-husband issue-what should I do?

[NoEffingWay]

Ex-h is notoriously unorganised. Ds's school are breaking up a day early, when DS is with him. They notified us via email and someone also posted it on the whatsapp group for the class. Ex-h receives both of these.
I get a series of panicked and angry messages today blaming me for him not knowing about this. My response is that I can't help out as I'm at work (true) and that he needs to sort it out, as he had the information available but did nothing to it.
Is this correct, or AIBU? He has called me all sorts of names and told me I am a horrible person, and that I should have reminded him again.

What an idiot!

What’s more - your son will one day be able to read them.

What an absolute dickhead.

Doesn't that come under "revenge porn" and is now illegal?

I did ponder this, I called him and shouted at him to take it down.

He tells me that by calling me 'my ex-wife' he didn't name me-I am his only ex-wife so it's not exactly hard to work out who he's talking to.

Report to the police

@NoEffingWay, fuck that for a game of soldiers. If he wants to pull out what he thinks are the big guns (the Twitter stuff), you can better him by reporting it to the police. Do it, or otherwise you are giving him permission (by default) to keep doing it. Don't live like that. There is no way he should have the upper hand. You've already recognised he's no great prize. Stand firm for the sake of establishing some boundaries for you and your DCs.