Send it back. The seller sold you a brick. Unless you want a desk ornament or a dedicated writing device (using the built-in Docs to Go), move on.
There are several reasons why you might want to remove the anti-theft firmware from your BlackBerry Classic: blackberry classic anti theft removal firmware
There is no "firmware" that removes anti-theft, but there is a procedural exploit using a specific combination of security wipes and autoloader versions. Send it back
There is no official "removal firmware," but community-developed custom autoloaders bypass methods are widely reviewed as effective alternatives Reviewed Removal Methods There are several reasons why you might want
The Anti-Theft Protection on BlackBerry 10 devices (like the Classic) is designed to make the phone useless if stolen.
If you are already on OS 10.3.3 and cannot downgrade, use this updated method to bypass the setup screen:
If you are stuck on the initial setup because of a forgotten BlackBerry ID, use this accessibility-based bypass: