Sorry man you're out of luck. The game see's you already received the car through their servers. The backup files don't backup until you quit your current game, so, seeing your PS3 was improperly shut down, it corrupted your save file and didn't get to create a new backup (with the car).
If your PS3 does ever freeze don't just shut it off right away, try playing with the PSHome button, sometime it un-freezes (defrost? lol). You should also quit the game from the PS Menu while in a game (hold down PS button, shut down system).