The verb you're using in this sentence is "starat se o něco/někoho"; it is reflexive and after the preposition "o" follows the accusative.
The preposition "o" probably confused you, because it can also be followed by locative (not in this case).
I'm curious... Would "He never took care of that" also be an acceptable translation? (If I'd gotten this as a Write This in English exercise, that's probably what I would have written.)
UPDATE -- "He never took care of that" was accepted.