No regard for bookings

We made a booking for a Friday night. When we arrived, the hostess told us that a booking is not really a booking and our table was not available. We would have to wait 45min for a table. What is the use of a booking then? And this has happened to friends of ours as well. As soon as the restaurant gets busy, they would give away your table and use the excuse that it was not really a booking is not really a booking. Very poor treatment of customers.