It’s best to first double-check that this isn’t a previous booking that was canceled and resold on Booking.com.
Auto-replenishment on Closed Rooms
You might have had a cancellation, where the room later went back on sale due to the "auto-replenishment on closed rooms" feature on Booking.com. This is designed to give you more visibility and boost your conversion on Booking.com. However, you can disable this feature on the Extranet (it’s found in Settings in the Property tab).
There might be a connection issue between your provider and connected channels like Booking.com. If you think this might be the case, it’s best to contact your provider who can look into this.