thanks all for yourreply, act. i can take my car to any service shop but this wont be a solution because i like to fix everything byself.
kdiesel
STP son of GUN is not working, i alrady tried that .
g16b
i have black wax but my dash is not black and i think black wax will mess with my grey dash.
AbidSiddiqui
mitti ka tail is also not working.
blueone
I think i should try yr suggestion, and hope i wont need to replace my dash 
anyway thanks all for helping me. i will tell u the result after using the vinegar and bicarbonate soda (backing soda).
Regards