Hello,
I bought the Logitech Car Pack and the payment went fine. But then an error showed up which said that
there had been an issue downloading the car pack. When I click on the Car Pack it doesn’t say “bought” and
would have to buy it again. But it’s already been paid via Paypal, so I’d like to get the cars please. 
Best Regards,
Benny
DLC purchases are the area for Xbox Live Support. Contact them and they will be able to verify the purchase and set things straight: Xbox Support
the cars are found in the free cars tab in the buy cars section…you don’t need to click on the buy car pack in game at all
try hard resetting your console if they arent there…also check in the game tab from settings that the pack has actually downloaded
im guessing you are clicking on the buy car pack in the game and not the xbox store