10 year car pack missing cars

I have the 10 year car pack dlc 9 of the cars are available to me in my garage. But one of them is not and that is the 2015 Mazda MX-5 in my cars it’s got dlc above it when you click the a button all that happens is A rotating circle please can some one help with this problem

The MX-5 is not part of the 10 Year Anniversary Car Pack. It was an exclusive car for pre-ordering FM6 digitally.

This thread should cover you with all the information: http://forums.forzamotorsport.net/turn10_postst38094_Forza-Motorsport-6---DLC-and-Editions-List.aspx

I did pre order the game but as said it does not unlock all I have is dlc above the car