my Facebook is intertwined with my mom's and can't log In to my phone now

it all happened when my phone broke. then after I got a new one but when ever I log into my Facebook with my email and password it signs into her profile. and I want to be able to use it since I turned 18 two days ago and want to use marketplace. but now everything is like they merged. it even happens to messenger. I was signed in, but when I could not get it to work I just deleted. but anytime she would get a call on it my phone would ring but not hers. and the app was completely deleted. the only thing that I can sign into is insta on my phone. I have no trouble with browsers just on here. how do I fix this? it's driving me absolutely crazy