Don’t worry they haven’t! The cars and tracks were designed to be locked again when starting a new save game in case you wanted to have the enjoyment of progressing through the game to unlock everything. So if you start a new save game the car and tracks will be locked at the beginning; if you want to unlock them all again, simply select the padlock icon in either Car or Track menu. You will see the standard message asking if you’d like to unlock them.
If you are asked if you want to buy the car and track pack again, simply select “Yes”. You won’t get charged again – you’ll just see a message telling you that you have already purchased it before and can download it again for free. (This will also happen if you have Carmageddon on more than one device).
Note: You will not be charged again providing you are using the same Apple ID that purchased the pack(s) previously.