Mods not working or how to get all the cars

I purchased most wanted because I had it years ago and wanted to play it again. I have been playing and it is working fine. Got it from Steam. I also purchased a few mods - Need for Speed™ Most Wanted Premium Modification Unlock and Need for Speed™ Most Wanted Premium Timesavers Pack because I was interested in doing this all over again. I just enjoy getting changed and outrunning the cops. My issue is that I am being asked to purchase some of the cars I run into. I thoght I already purchased that. But maybe there is more so I go to the store on Steam and it tells me I already have it. So how can I get all the cars?