From the post it sounds like the person who picked it up wiped the laptop and set up activation lock with their own account.

Ah that makes sense.

That might explain why Apple won’t deactivate it. They don’t have a way of knowing if the OP sold it to someone and “stole” it back.

If the guy who got is legit OP may want to reach back out to that guy and ask him if that’s the case the guy who had it may be able to disable it from Find My.

I'm confused about it to. I suggested some possibilities in the "How did it get locked in the first place?" of the article.