Hotmail account compromised: malicious forwarding rules keep returning

My personal Hotmail/Outlook.com account has been compromised. I can still sign in, but I cannot permanently remove malicious inbox rules that forward incoming emails to an unfamiliar Gmail address.

What is happening:

• A malicious rule named “idtienphuoc1” reappears approximately one second after I delete or disable it.

An additional similarly named rule appeared.

I created a rule above the malicious rules to stop further rule processing, but my own rule subsequently disappeared.

• The account language was also changed.
• When I try to edit the malicious rule, Outlook displays a error message meaning: “The operation could not be performed because the object ‘[rule name]’ could not be found.”

Security measures already completed:

• Changed my password on a different device.

Enabled two-factor authentication.

Used “Sign out everywhere.” The stated 24-hour period has not yet elapsed.

Checked application permissions: the list is empty.

Checked registered sign-in and verification methods: all belong to me.

I currently access Outlook.com through a web browser and do not have Windows or classic Outlook for Windows available.

Could a Microsoft moderator or support representative please explain:

How can these malicious rules be permanently removed from a personal Outlook.com mailbox when deleting, disabling, and editing them fails?

Could the “object not found” error indicate a rule synchronization or server-side issue?

How can I open a private technical support case when the documented Outlook.com email-support option is unavailable?

Thank you very much.