How do i stop my parents from snooping through my chats

I'm 16 F still studying, and i've noticed that my parents (mum) go through my chats with other people while i'm asleep. Today she brought up a chat of mine while we were having a convo, it was something that i did not want her to find out then she said something along the line of 'you're lying to me' and somthing like 'you're hiding stuff from me' and got all emotional. to be honest at that point i felt so violated, because she had snooped through my chats with my friends. [The chats were about the new changes in the insta feed] although i know her doing this is just looking out for me but tbh it gets to a point, and doing this all the time just made me feel so objectified like as if i'd do something wrong if she wasnt checking. Should i resort to deleting my chats after i'm done talking with the other person?

Update: i cant really put a lock on this current phone that i have as she will demand the password so i have resorted to deleting the chats right after i'm done talking so that she doesnt find out what i'm talking about. Thank you all for the advice, you all helped me a lot!