My account won't let me sign back in even with the correct information.

I have had this xbox account for a long time and haven't had issues with it before however at some point it has signed me out of my account on xbox. When I try to sign back in it asks for the microsoft account witch is connected and the password however when I put these in I get signed into a random account I haven't played on witch has no data or achievements.

At first I was worried my account had been overwritten by this new one but my old account still exists as I've been able to add it as a friend on my alt.

I also thought that I might be using the wrong microsoft account, which is my mother's, as ive had this account for many years but when she signs in to her microsoft account it show up as connected to my accounts username.

If anyone has suggestions to help I would greatly appreciate them otherwise I would lose a decade's worth of game data.

:)