Perhaps you need to look at the Airbnb calendar. Go to the dashboard and on the left, under your photo, there is a box. Click on View/Manage Listings, then click on your listing. When that opens, there is a small box on the upper right that says View calendar.
Each time Airbnb confirms a booking for you, check to see if those dates are blocked. They are blocked in blue with the first name of your guest. Another guest cannot book those same days.
If you are accepting bookings from another company, you cannot list the blocked dates unless you are properly linked. So you may need to block those booked dates yourself. Always check to make sure you have identified a starting date and ending date, and then click "blocked" on the top far right of your screen, then "save".