I have 14 installed car packs but none show up in my garage. I have downloaded them as free and they did Not show up. I contact Microsoft Xbox support and they had me uninstall and reinstall. Now the cars are back in the auto show but don’t show up as free. My game (disc) came with a code for the tenth anniversary pack and it suffers they same fate. Microsoft support sent me here.
Check this thread here.
https://forums.forza.net/turn10_postst30285p2_-ANSWERED--No-free-DLC-cars-with-car-pass.aspx
A staff person gives instructions that may be of help.
Have you checked the ‘free cars’ tab inside the buy car menu ???
They don’t go directly into your garage …