|I have purchased two figs trees recently.; lovely they are. 1|
|Ficus trees are typically problem free so I wonder what's going on with yours? It is normal for fig trees to drop their oldest leaves, those toward the center of the plant, in favor of producing new leaves at the branch tips. Very dark green leaves indicate they are drying out - maybe from not enough water - or that the root mass is waterlogged which is excluding oxygen and killing off the leaves. I would double check the soil to make sure that you're watering thoroughly when you do water. Sometimes plants in containers can develop air pockets around the roots and even though you think you're applying adequate water, some of the roots remain high and dry. To counteract this tendency, occasionally immerse the container in a larger container of water and let it sit until no more air bubbles rise to the surface. Then remove the container and allow the excess water to drain away.
At this point I think I would prune away the affected branches. The dark green leaves with black spots will drop on their own, but pruning the branches back will encourage the development of healthy new leaves along the remainder of the branches.
Best wishes with your fig trees!