You may not be able to check the settings on your smartphone or tablet, so be sure to check the settings on your computer.
Please click [Settings] (gear icon) in the upper right of the screen, click [View all Outlook settings], and check that all the settings are recognized.
Especially, the following 6 items are highly likely to be abused by an attacker who stole your ID/password, so please check them carefully.
[Account]-[Automatic replies]
[Account]-[Mobile devices]
If your device is listed, click the pencil-shaped Edit icon and verify that the registered device is one you recognize.
[Mail]-[Rules]
[Mail]-[Sweep]
[Mail]-[Junk email]
[Mail]-[Forwarding]
Please make sure that the Add-ins contains only what you have registered.