First, China Doll is a plant that does best with bright filtered light indoors. It is very sensitive to under- or over-watering, resulting in the leaves dropping off. It is very sensitive to moving to new locations, so the combination of moving to your home, the repotting, and overwatering put it in shock. The result is leaf drop. Since the leaves are black, this leans toward overwatering. Underwatering would result in dry, crispy leaves. Cut back on the watering if you have not and only water when the soil had become dry. Give it time to readjust and see if new growth develops. Make sure there are drainage holes in the container and don't fertilize until you get new growth. Since we're going into fall/winter, houseplants in general go into dormancy and don't need feeding. If the plant doesn't produce growth to form a pleasing plant, you might have to discard it and start with a new one. It may never regain the fullness it had when you purchased it.