it is clear that the mechanism for getting rid of the mark is broken or still missing an ingredient. try painting with pharma grade sodium ascorbate and see what happens. might even soak a bandage in a strong solution and tape it on the spot.
its probably a basic which leads to lack of circulation. what you see on your skin is how your organs appear, too. hydration, oxygenation, circulation and nutrition. one of these is missing or inadequate.