Disappointed!

Hi, I have made a reservation for my birthday at the Grand Cafe Waterfront. I have informed them that i am awaiting for my guest to respond (RSVP) and i will revert. I got confirmation of my guest and got in touch with The Grand immediately. I sent them an email last week, to which they have responded today and said "Unfortunately, we now have a confirmed exclusive event on the 06 & 07 January. They did not make any contact with me to confirm whether I will be canceling. This is unprofessional and unacceptable! I have already sent the invitations to my guest, what do I do now?? This is the worse thing ever!! Not a good start to my New Year!