Restrictions

Hi so i am fifteen and my parents have decided that they should know my password and are allowed to go through my messages and anything they want at any time they want. I told them that I should be allowed my own privacy but they won't listen and have put restrictions on what apps I use and time limits. Earlier they went through all of my messages, dms, and into every app I had. They say I get privacy when I turn eighteen but I think it's unfair. They are even allowed to go through messages with my bf. if I say no I get punished and get my phone taken off me. It's making me really sad and annoyed because I just want my own privacy. I have done nothing to make them angry or want to do this, they just decided it out of nowhere. this really necessary of them and should they be doing this???