Should I talk to my principal?

I"ll try to make it short. They were going to give me more hours of work only this year because a coworker is leaving, just this year. I work in a highschool, too so I asked the principal to change the schedules. It's not a favor, they are supposed to do this everytime there is a change.

He said yes, I'll talk to the person who does it. Next year I talked to the vice principal and he said"no, the principal said you were going to have the classes you could and the other ones we are going to give them to someone else", I was like what?! If I work here the rules say I should have those hours and if there's noone they can call someone else. So I accepted to have less hours than I thought (to be honest it's fine, having those horrible schdeules and not having time to rest it's anightmare, going fron here to there etc".) But it bothers me that he lied to me, and I dont wqant him to think I want to fight or something. Plus the viceprincipal. Is an idiot and i dont want him to be there when i talk to the principal,and I dont know how to say or how to bring up the topic. What should I do?=S