Facebook Messenger connects automatically when I unlock my phone.

Hello everyone, so here it is, lately my cousin told me that I was connected to Facebook all day long while I was at the store without going on the internet! I borrowed her account and realized that every time I unlocked my phone to reply to a text or something, the Facebook Messenger app would connect (therefore) my Facebook account was online. So I did what everyone advises, changed my password, logged out of all devices from my account, even deleted the app data, deleted the app, and reinstalled it, but nothing worked; it connects every time I unlock my phone! And even with my old phone, it did the same thing, so it’s the app that’s the problem. Do you have this issue? Do you have a solution to keep the app without it connecting by itself? Thank you very much.