I am so so sorry this has happened to you, how awful!!!
I hope you will be getting something out of Airbnb, but these days, you probably can't count on it.
For your own good, if you continue hosting via Airbnb, I would immediately turn off the instant booking you have in place, and also change may cancellation requirement from flexible to moderate.
From reading some horror stories here in the forum, it seems to me that these things happen when nobody, certainly not the host , is around. It just seems too risky these days. Could you possibly find someone to go by each day you have guests there, possibly with an excuse to bring new towels, or whatever, to go by the place and check on things? and if the guests are not there, just get in with an extra key? Whatever you would have to pay that person, add it to your rental price.
I sure hope you won't have to deal now with the consequences of cancelling the next people, like having these dates blocked and $$ penalties leveled against you.
my sympathies,
thanx for the heads up on this, I hope you got the police involved, took pictures, and absolutely, flag these people and insist Airbnb banish them. If not , at the absolute minimum, give them a terrible review.
Annette