You typically have 2 options when it comes to a stolen license.
1) Contact theAutodesk License Assistance team and request that a new one be generated and the old one be inactivated. As you're already here you can do so by simply sending me a Private Message (click on my philip.s profile name and then "Send this user a private message") with your serial number.
2) Report the issue to the Autodesk License Assistance team and request an activation code and that a note be added to the license. Any subsequent activation requests would be blocked by a user other than the registered party.
Please accept as a solution if this fully resolves the issue, or reply with additional specifics as needed.