You are Italian, right? Have you checked with the community over at http://www.amicitreni.org/? They might be able to help you in your own language, without barriers.
Anyway, it seems you miss the whole of the Kuju folder.
Please open Windows Explorer, navigate to your Steam folder. Open steamapps/common/railworks folder. There should be an Asset folder, open that as well.
Now look for a folder named Kuju and open that. Inside you should find three folders: Railsimulator, RailsimulatorCore and RailsimulatorUS.
Since we are dealing with a USA route here, open the RailsimulatorUS folder. Inside you should find a RailVehicles folder. Open that and look for the Freight folder.
Inside the Freight folder there should be folders for each type of freight car. Those freight car folders must not be empty.
Now go back up to the Steam\steamapps\common\railworks folder in Windows Explorer.
Start the utilities.exe program and wait for it to open.
Click on the Package Manager tab in the upper row and once the package manager window is open, click on the Refresh button on the right.
After a while there should come up a list with all of the DLC packages you have bought. Any illegal packages won't show up.
Compare this list with the list you get when you open the DLC tab from the black Train Simulator 2013 - Properties window which you find when you right-click on the Train Simulator 2013 entry in the Steam libary of all the games you have bought.
NEC and all your other assets you've bought should be visible in both windows.
This community is here to help you, but probably all of us old-timers have bought the previous versions of TS2012 etc. so our experiences are different.