Did you speak to your SM?

Probably a misunderstanding. Do they know you are on break? Many people verbally open up their availability when on break, they may have assumed your limits were only due to school obligations, or gotten mixed up during the holidays.

So if you need a set schedule make sure to communicate and bring it up as needed. Definitely address it before you go back to school, is the class schedule the same as before? You don't want or need to stress about missing a shift because of a class.

Uh talk to them? I feel alot of the questions on this subreddit can be fixed if you just communicate with the other human being. As long as u make the attempt, then if they're an ass, at least u tried and u report them to ethics AFTER

Talk to them. Sometimes SMs are under a lot of stress right now and are bound to make mistakes. Now if they don’t fix it that’s another issue

Don't show up until a time that fits into your availability. You already told them what times work for you it's not your fault they're setting shifts outside of that

contact the dm