Do you think this is fair?

My sister who is twenty two moved out about a year ago on her own choice. My mom has been promising me here room for months and I just got it three weeks ago. I really want this room because I need more space for studying and I need more room for my books since my mom won’t get me a book shelf. Well see my sister has really messed up and isn’t in control with her life and my parents have been giving her so much it’s not even funny. This room is the only thing I have since my parents don’t even pay attention to me anymore. Well now my parents are going to make me move all of my stuff back into my tiny room with a twin size bed, and out of the big room with a queen size bed. All because of my sister who has messed up needs to move back in. So was telling my mom today how she is breaking her promise she said this was a promise she needed to brake… Is this really fair? I don’t think it is but I don’t know I just want someone else’s opinion. So is this fair?