The matter is that each platform just imports bookings from external links you placed. Thus Hotel Booking plugin imports bookings from links you added as external calendars. Make sure you have added your bookingCom links to Dashboard > Bookings > Sync Calendars. Also you may open ical link in browser and save ICS file. Then open it and check if blocked dates are stored there. If you can find the blocked dates in the ical file of bookingCom then hotel booking plugin should be able to import such bookings.