Britannia on William, Perth

I booked a double room 1 month before leaving to perth, over the phone with David, one of their night staff. He confirmed that it was OK and I even asked him if he needed my credit card number. He said NO, that the room was booked for me. I asked a second time if it was guaranteed that i would have a room and he said YES, also I gave him my e-mail to contact me in any case! Well, end of the story is that I called them 1 week before travelling to reconfirm and another person checked my booking and said she could not find anything under my name and they were fully booked for the period I would like to stay. What a shame on them.