I park my Hyundai Santro in my flats open space Some

I park my Hyundai-Santro in my flats' open space. Some residents in the upper floors have done some post-rain, maintenance jobs in their apartments, with WHITE CEMENT and perhaps, poured some power/liquid of WHITE CEMENT over my car's rear-wind shield.

On a routine water wash, they are stuck still and an ENAMEL like soot/dust is layered on my car.

How do i remove it? What type of a WASH / TREATMENT should i resort to?

Help please!

Thanks