u can use soft 99 or any car polish.. but must not hand polish... need buffing machine. or else just go to your nearest car wash that offer body polish and pay them to polish your windscreen.

clean n slippery

rm150 rip off,
go to other shop pay them 80 is more than enough

if u want cheap diy, use cutter knife , the small one, and scrape the spots .
there is no point me helping you on how to negotiate because u don't have the basic understanding and u can't win argument over with them, your only best option vs them is tell them take it or leave it and u keep searching for next car wash.
I read that u actually use soft99 to polish it without results..
possible explanation is you use your finger to rub it or u didn't do it the correct way.
correct way is to rub using your palm in circular motion. with firm pressure.