Outraged!!!!!!

I booked a place at Shimmy on 12/02/2015 for 10 April 2015 for our team social and farewell party for 9 people and Nadine(the junior Events coordinator) confirmed the booking letting me know she booked the restaurant for us and as per her email there is no fee for us to pay and after we have eaten we can move to the lounge (please note i still have all the emails confirming this). She then comes back to me on 18/03/2015 letting me know she FORGOT that Showtek will be at Shimmy on the 10th April 2015 and therefore we should either buy tickets for the show or alternatively move our date. I let her know we cannot move our date as we have arranged with our Company already and there are people leaving our team so that is the only day we have to go out. She clearly does not care that IT WAS NOT MY MISTAKE BUT HERS. Why should we suffer because of her mistake and because she clearly didn't do her job properly? i don't want long stories - i want someone on management level to contact me and tell me we can still come on 10 April 2015 without any costs as arranged with Nadine on 12/02/2015. Our company is very disappointed with the service received. Bad taste in our mouths !!