Open live, click the cog in the top right hand corner and make sure nobody has set up email forwarding, if so and you don't recognise the address, move the slider left to turn forwarding off.
Next top right hand corner, click initials (or pic), click My Microsoft account > Security > Manage how I sign in
Make sure under email a code, only your email is there (check view activity too)
If you haven't already and want to MFA just follow the instructions under this link and use Google Auth again
Click Your Info
Make sure the email addresses and phone numbers are just yours. Remove anything that isn't yours with edit account info