My email was hacked.

If the account was hacked, secure it first, then address the folders.

1. Run the Microsoft account recovery/sign-in helper if there is any sign of ongoing suspicious access: Start.
2. Before making more account changes, run a full malware scan on the PC. In Windows Security, go to Virus and threat protection > Scan options > Full scan > Scan now.
3. Review account settings that attackers commonly change and remove anything suspicious:
   • connected accounts
   • forwarding
   • automatic replies
4. Try deleting the foreign folders in Outlook.com on the web:
   • In the folder pane, right-click the folder or subfolder.
   • Select Delete.
   • Select OK.
5. If the folders still cannot be deleted, check whether they are default folders. Default folders such as Inbox and Sent Items cannot be deleted.
6. If these are leftover folders created during a language change, rename any existing folders that match default folder names in the other language so every folder name is unique. Then in Outlook on the web go to Settings > View all Outlook settings > General > Language and time, choose the preferred language, select Rename default folders so their names match the specified language, and Save.

If the preferred language is already selected, switch to a different language, save, then switch back and save again.

References:

• How to recover a hacked or compromised Microsoft account
• Working with message folders in Outlook.com
• Cannot localize the default folders error when changing default folder names to another language in Outlook on the web
• Issues with default folders in Outlook