similar thing happened to be but only a scratch on the bumper. . . paid police report coz it is needed to file for insurance (no fines there). . . I did not pay the QAR500 before. . .

but now, with the insurance (law), per claim you have to pay QAR500 (your fault or not)

if you found said bus (take a picture of your car and print it big). . . then you have to report to the police (jot down the plate no.) so that they will pay for the damage of your own car

good luck, detective ;)