Unprofessional service

My Brother in law and I have been planning a shower for my sister. We decided to go with Cafe Hemingways because we it had good reviews. Everything was exceptional,from venue to cakes. There was no compromise, was a perfect choice. We went ahead and booked the venue for the 3rd of December and got confirmation right away.The level of excitement could not be contained.Everything from venue,food, cake was checked off the list.There was just decor that had to be arranged and finalise the cake design.A day later I get a call saying that they made a mistake,someone booked the whole restaurant which means I am out and I need to make other arrangements . These are the same people who were excited to host us and confirmed the event. This is unprofessional and they broke their first come first serve privilege because they wanted to make more money.I am a few days into exams,all the way in Stellenbosch,have to explain this to my guests and find another venue in Johannesburg.