@Iain24 You have an amazing listing and wonderful reviews. I'm going to be honest, I did not expect that from this post, which is somewhat breathless. I do believe every word of it, but can't quite sort it out. Okay, first things first:
* Really, really sorry you're battling cancer. That's terrible.
* Have you reported the profile of the offending guest?
I'm not completely clear on what you've asked Airbnb to do. Are you asking them to remove the offending review? To ban the guest? To reinstate your SuperHost status? To get you more bookings or to put your place higher up in the rankings? Can a lawyer help with any of this?
While you are trying to get help on those things, I would suggest you reach out to Airbnb via Twitter (@airbnbhelp) and request that they confirm your settings: 48-hour advance notice, NO instant bookings, and any other important settings. Keep this request separate from the other thing, if possible. If they come back to you and say yes, confirmed, you will have a message thread with them in case the settings go awry again.
Finally, if I were a prospective guest, I would dismiss Asia's review. It's lost in a sea of incredibly warm, laudatory reviews. So don't stress that part of all this. And maybe raise your price for awhile to weed out the riff-raff? I would just make it $60 a night for a month and see what happens.