Well, if it wasn't a game but real life, I could recommend a reliable locksmith to you. I often turn to him, and he solves all my problems with keys. But since this is only an online game, I assume the fact is that you have not completed some quest or have not reached a sufficient level of character levelling to unlock the car. Think about what exactly you did not do or did not do at this level, and then you will be able to unlock the opportunity to start a car. Good luck to you!