Motor cars are covered by the Consumer Protection Act and you are fully entitled to the full protection of the above Act.
Your used car must be of good quality and usable for a reasonable time, there is no specific time mentioned but the car should have a six months warranty against defects.
The consumer does have a right to request a refund if the vehicle is not of good quality or in a reasonable and drivable condition, keep in mind that you must have a good and legitimate reason to request a refund.