Hi Valerie,
You must have "Instant Booking" turned on in your Listing. This allows Guests with the correct Airbnb criteria to simply book in without further reference to the Host.
You can untick the "Instant Booking" box in your listing to stop the above from happening.
Cancelling a booking without a very good reason is big "no-no" as it disrupts guests travel plans enormously and is viewed seriously by Airbnb.
It is because you have canceled a booking that Airbnb doesn't want further guests inconvenienced so have blocked your listing.