The old display name would have been reserved for six months EXCEPT if the hijacker did a double name change. A double name change frees the name up immediately.
You need to review your email, device and account security. There should be no way a hijacker can enter your account.
Please work through the instructions on the
Security tips
support page.
Also, check the 'Linked Accounts' tab in account management and unlink any accounts you see linked. Click on 'Manage Steam' to check for a linked Steam account.
I am sorry to say it wasn't stolen. You just made a mistake.
Have you tried to get it outside the game?
The richest person is not who has the most. It is who Needs the least.