Strong reaction to Cosmelan/Darkened face and neck skin.

I have brown skin. I had cosmelan treatment for an old scar i got years ago from post laser treatment sun exposure. The scar got removed but then I had strong sun reaction and now both skin and neck have darkened. It seems superficial as it goes away sometimes with sunscreen use. How to remove it permanently? I am talking to a dermatologist and she says I should stay away from more surgeries as my skin gives strong reactions to it. But i need results! The creams she gives aren't doing much.