Getting treated like a little kid (again)

Last time I was treated like this I was 8 years old. Well now it's happening again now that I'm 11 probably because I'm new to an older kids class, but still they're going back to the way I was treated in grade school and this time should be different more teenager thing kind of stuff to be scolded to wait for when I'm older not this crap. So once they thought I was recently 9 and just turned 10. Wtf I'm 11 in a half nearly 12 no where close to younger 10's. And these girls? 13-15 years old one time Izzy asked me an embarrassing question in front of the teenagers saying "Helena aren't you gonna come into my class?" The class was for 3-10 year olds. The class I was in was for 11-18 year olds. I responded "No that's the grade school class and pre-school class I'm too old for it" then Billy the teacher laughed and Remy said "you don't really get too old for that class till you're like 16" I thought "Seriously? Look around you there's a miniature dollhouse,kiddie tables, plushies, kids books, toddler tunnels, teachers that won't allow you to leave the classroom without an adult unless you have to use the bathroom, little people toys for babies, and toy cars!" I was allowed to leave the Uniteen room by myself until.... I wasn't allowed on my phone even before class started so I went into the bathroom and before I could even open the door Bill said "where are you going?" And I said bathroom. So we're in the room and 2 of the girls are eating cinnamon rolls and I was hungry I couldn't have one since I was gluten free. Then I remembered the black berry bush it tasted good. So I went outside to get some and then Bill yells at me and says "Helena! Get back here!" And I thought that he trusted me alone, apperently not so then I heard they were serving ice cream so Mia and Sidney were serving it and they gave me 1 scoop and I looked at them thinking where's my 2nd and 3rd scoop? They just stared at me like why you still here? So I try getting more myself. And then Sidney says "Honey let us do it at least" and Mia comes in and says "Only 1 scoop!" I can't really stick up to Sidney she's bigger and she has the scolding of an adult. But even though Mia is 13 or 14 she's small for her age and nearly my size so I can stick up to her a little bit. But I just walked away in digust.