If your country's iTunes Store allows you to redownload purchased tracks, I'd delete your current copy of the track and try redownloading a fresh one. See the following document for instructions:
Otherwise, I'd report the problem to the iTunes Store.
Log in to the Store. Click on "Account" in your Quick Links. When you're in your Account information screen, go down to Purchase History and click "See all".
Find the item that is not playing properly. If you can't see "Report a Problem" next to the item, click the "Report a problem" button. Now click the "Report a Problem" link next to the item.