Hello @TheMelbourneHome0
Have you received confirmation from Airbnb showing the booking has been cancelled and your calendar is open?
It is incredibly rare that Airbnb would cancel a guest booking once it is underway, where there is no host complaint.
So I would hazard a guess that either their payment hasn't gone through (less likely as they normally try and resolve, or they know it is a fraudulent booking or they have become aware of some previous criminal activity on behalf of the guest.
This is a civil matter and one for you to resolve as the business owner. You can't expect to use your local police force resources for a business matter.
Presuming you have confirmation from Airbnb that the booking is cancelled inform your 'guest' that you will be coming over to help manage the check out process with them, remind them of your check out rules and time. Tell the guest that you can see the booking has been cancelled and that they need to take up any issues regarding this with Airbnb.
Make sure you bring a witness and photo/video the apartment noting any damage.