Usually when a seat doesn't latch, I check for objects and seat belts obstructing them from fully seating (no pun intended). After that, I give it a good whack until it latches. But your problem sounds more involved than that.
If the latch really no longer moves, I would bring it to the dealer to let them sort it out.
"Why would I want to profess my feelings for some 3D girl?" - Tomoya Aki from the anime Saekano