Well, the problem is not that he’s tweeting, the problem is that once again the facts tell otherwise (except the military base). The tax claim is false as is the devaluation. However, he’s right that it is outrageous that China wants to forbid the president-elect a phone call.
No one is "forbidding" him anything. It's just that he's demonstrating either reckless judgement, or a mix gross ignorance and stupidity (or all of the above), and then compounding it by whining like the petulant man-child he is. None of which should come as any surprise.