iTunes works so well that most people will never need to report a problem. But, computers are only human, and things go wrong with downloads sometimes, so it's good to know how to resolve a problem with iTunes. I have had problems with files sometimes and iTunes has resolved them very quickly, either by giving me a refund and arranging to have the file(s) downloaded again.
To report a problem with an iTunes file, you will need to go to your "Purchase History". There is a link on your email receipt that should take you directly there. This is the what the "Purchase History" screen looks like.
If, for some reason, the link doesn't take you directly to "Purchase History", you can get there by clicking on your login name (at the top left of iTunes). It will ask you to log in again, and click "View Account"
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