DLC cars are still locked online as I have already bought the Deluxe DLC package

I bought the Deluxe DLC package, but in the game the cars showed locked still. I asked help with “Contact Us”, but the specialist there said that he can neither unlock my dlc cars. He asked me to post an article here. By the way, I have played the game for two and a half years. And I have ran the game hundred of times. There are surely several times I could drive the dlc cars, but probability that I could drive them is about 1%. If I closed the game, next time open the dlc cars are locked again. Could someone just help me!