Booking.com books accommodation when there is none!!!!

I am extremely disappointed with booking.com. Yesterday I had made reservations at the Hilton hotel via the site and according to them had plenty of rooms available. After having gone through the process of booking, getting a confirmation email and a pin to secure my reservation, I go to the hotel only to be told that there were no rooms available. The staff were unsure as to why booking.com was still taking bookings. Not just myself but a few people checking in with me also had to be turned down. An absolute waste of my time. All plans had to be cancelled and what an inconvenience to me having made my way there only to have to go back home. Please do not use the service...rather go personally as they are not dependable!!!! Imagine if I had come all the way from another city or country. What's the use having the site if this is what they do!!!!