Hi Cynthia,
I'd recommend you change your password and enable two-step verification:
Turn two-step verification on or off
Go to the Security basics page and sign in with your Microsoft account.
- Select More security options.
- Under Two-step verification, choose Set up two-step verification to turn it on, or choose Turn off two-step verification to turn it off.
- Follow the instructions.
Note: As part of setting up this account, you’ll be given a QR code to scan with your device; this is one way we ensure you are in physical possession of the device you are installing the Authenticator app to.
If this is helpful please accept answer.