Drumpf only has himself to blame. If he'd use the POTUS twitter account, as he is supposed to, for his presidential bleetings, he could ban whoever he wants on his personal one. But since he insists on using his personal one for official business (lock him up?), he is not allowed to prevent people from viewing his inane ramblings.
But as for Ocasio-Cortez, I don't think AOC's speech is required by law to be viewable by all, like the President's is. IANAL.