Dear Riddhima Minocha
Thank you for posting in the Microsoft Community.
You can hide your original account name by changing your primary alias so that hackers don't know what you're logged in as now. So the hacker will get stuck at the Enter Account screen and won't be able to reach the Enter Password or Security Verification screen at all. It won't try to log into your account and show a failure.
- Add a new alias, change this alias to the primary alias. You can add aliases through this link. Add or remove an email alias in Outlook.com - Microsoft Support Notes: Do not delete your original alias.
- Uncheck the original account name in the sign-in preferences so that when you log in using your original account name it will say this account could not be found (The fact is that the account doesn't cease to exist, it's just hidden), so that hackers can't attack using your original account name. But you will have to log in using your new primary alias as well. So you may want to keep your new account name in mind. You can take a screenshot and save it.

Since the recent activity shows that the hacker did not succeed in logging into your account. There is no need to worry too much according to. They just used a special cheat to mimic your email. It looks like you sent it to yourself. In fact, it's not.
I hope that my reply will be helpful to you.
Please feel free to let me know if you have any further updates, thank you.
Best Regards,
Simon - MSFT | Microsoft Community Support Specialist