I spend a lot of my life in long-term stays. The policy is very clear: once I make the reservation, if I cancel it then I owe thirty days. Period. It doesn't matter if I cancel the day before the reservation nor an hour after I make it. So I need to be very certain before I reserve, as I will be out a lot of money if I change my mind.
As for the $200 they requested, it's possible they were trying to scam you. If they communicated this via the Airbnb message platform, then I would advise you to report it to Airbnb. If they communicated in any other way, such as by text or email, you can't prove it was them. You did the right thing for yourself by not giving them the $200 or you would have been out even more money than you are now.
I'm sorry the rules are not on your side and that you're out so much money, and I'm happy that you wisely protected yourself from a potential scam.