Rude sales person at popcorn station

I'm a frustrated customer with cinecentre liberty mall, on Saturday night I went to watch a movie, so went through to buy my popcorn for the movie and firstly a very rude sales lady helped us, secondly she took my order wrong yet I had witnesses who heard my order, when I tell her thats not my order was very rudely told that my order is already rung up on and I can't change my order to my knowledge there is something called a void, I'm totally annoyed at the service that we got on Saturday night and I do hope that management will do something about this