Most of the people on these forums, including myself, are fellow users - you're not talking to iTunes Support here.
What sort of purchase was it, an app, song, film, in-app purchase ... ? If it was on your phone then music and audiobooks should have downloaded into the Music app, films and tv shows into the Videos app.
You've checked in the Downloads tab in the App Store or iTunes store app in case they haven't finished downloading, or the Purchased tab to re-download them ? And depending upon what the item was then is it hidden by an age rating in Settings > General > Restrictions ?
If you can't find it, and it's not waiting to download and you can't re-download it, then try contacting iTunes Support via the report a problem' link from your purchase history : log into your account on your computer's iTunes via the Store > View Account menu option and you should then see a Purchase History section with a 'see all' link to the right of it ; click on that and you should see a list of your purchases ; find that item and use the 'Report a Problem' link and fill in details about the problem (iTunes support should reply within, I think, about 24 hours).
If the 'report a problem' link doesn't work (it's been taking some people to this site on a browser instead of showing a form in iTunes) then you can try contacting iTunes support via this page : http://www.apple.com/support/itunes/contact/- click on Contact iTunes Store Support on the right-hand side of the page.