To go to college , i can take a bus / public transport but cases of harrasement are very common there So , My father has an official driver and my father has kept him to drive me to college , i sit in the backseat . Is it khalwah?

Sitting in the back seat does not remove khalwah, being alone with him in the car is the khalwah itself. The scholars said what removes it is a second woman being present, or another man besides the driver, with hijab and with no suspicion. But, of course, do not go back to a position where you will be harassed.