@Marin36 Wait, your apartments are called Pink and Floyd? That's genius!
That's beyond annoying. Just keep fighting with them. They shouldn't be allowed to take money out of hosts' pockets. I had two cancellations this summer and I refused to allow full refunds for either, even though Airbnb asked me many times. However, your case is different, because Airbnb has already refunded the money without asking you, AND has blocked your calendar - it's insupportable. Yet it's true that they do not have to tell you why. Which has driven many hosts nearly mad.
Anyway, does the guest have any proof at all that you threatened them? That's a serious charge and just horrible that a guest would do that just to get their money back. Keep fighting.