You report “5 networks, 19 phones, 42 email accounts”.
That’s an immensely expensive and clearly failing fix for an immensely expensive and persistent security compromise, or maybe there’s something else going on.
Whatever might be happening, it is not going to get addressed around here, or in any other forum.
And it’s not going to get addressed by a sixth network, a twentieth phone, or a forty-third account.
Or by any advice that can be offered via a forum for that matter, having undoubtedly already been provided with that information, and having acting upon it as appropriate, and failing.
It is clear that whatever is happening here is not being resolved with your current strategy, though.