"Turn your phone" doesn't work

Every time I start a study session, there's a giant notification on my screen that says "Turn your phone. Rotate phone for landscape angle." No matter how many times I turn the phone sideways, it doesn't work. It's stuck in the vertical mode. I also can't close the notification, so I'm unable to access the chat, music button, etc. Please let me know if this happens to you too and if you know any solution!