I'll go to Calcutta on 20th August. My flight will land around 13:00 hrs. Will I get a volvo for Newtown ? or I should book an Uber ?
Yes you will get AC Volvo buses from near Airport Terminal at that hour.
Look for these two:
AC37A to Garia, Via New Town
AC43 to Golf Green, this too via New Town
There may be others too, just ask the driver or conductor or look in bus's display board.