I played the demo and everything, I even got a message saying “Congratulations, you have been gifted a Ford GT. Get it from the message center” or something like that. But so far in the “gifts” section, No Ford GT!
So it hasn’t appeared in the free cars section and its not already in your garage
Its only 250000 to buy
And to get the achievement you actually need to buy it
Could always sell it again for 125000
Its Not a solution to your issue…just a suggestion
Exactly the same issue for me. Got the same ‘congrats msg’, but then no car has showed up in the gift messages or my cars garage 
Had the game for about a week now. Thought there might be a delay, but now I’m just thinking it’s not going to happen at all!
You guys are not alone, for I myself am in the same boat as all of you. So not really sure what is going on regarding this, but really hope it gets sorted out soon.