Talk to Dermatologist on Depigmented Patch On Scalp

I had developed a strong hair dye alllergic reaction 6 months ago causing redness and itchiness of scalp and that was more concentrated and severe at one specific area. Later on hair shed in an oval patch at that location and turned into a depigmented patch as shown in attached picture of the same. I have tried all sort of anti bacterial, anti fungal, steroid oinment/creams etc but condition has not improved a bit so far. However, condition is not spreading further and there has not been any irritation, itchiness or pain since the first week of when it had happened. Need your expert advice on how to treat this.