Oak, I used to have the same problem when I worked at a restaurant around my way. I wound up quitting before I went on vacation though.
They were dicks to me. Say Tim says he can't work, well they would erase his name from the chart and put mine in b/c I was new and then when I question them about it they denied it. Well on my last night, I wasn't supposed to work, but they said I was scheduled. Well my asshole manager said something to me about not knowing if I could work Sat. night and to get my shit together. I turned around and just flipped on him and starting yellin shit like "Don't tell me to get my shit together, why don't you learn how to make a fuckin schedule that works and when someone calls out don't fucking call my house saying I'm late or I have to be there in 15 minutes b/c I know when I'm scheduled." He went to say something back to me, but I told him to shut his face and walked away. He wasn't going to fire me on the spot b/c he'd be out of a worker for the night. Turns out my friend was sitting on the steps out of site listening to my schpeel and told everyone at work. Now noone respects him and tell him off when he gets pissy.
Moral of the story: You got balls, use them. I used to be afraid of my manager b/c he was big and shit, but then I realized he can't hurt me and the worst that can happen is I get fired and go find another job. Put your thing down when you want something or they'll just walk ovdr you.