[vitovito]

If you still have your proof of purchase (if you bought it from Apple directly, they should also have it), you can take your receipt and the laptop to an Apple Store and they'll remove the activation lock. They may wipe the machine in the process, I don't recall.

(We had some company iPhones in our device lab, not on MDM, and people would attach them to their personal accounts, so this was an occasional hassle.)