There isn't a cart, you either buy an item by clicking on its price, or you can add items to your wishlist by clicking on the downward pointing arrow to the right of the price (you can then either leave them on your wish list, delete them from it, or buy individual items from it).
Does anything show on your purchase history : http://support.apple.com/kb/HT2727 ?
Or is it on your wishlist : http://support.apple.com/kb/HT1368 ?
If it has been purchased then you can try the 'report a problem' page to contact iTunes Support and see if they will credit or refund you : http://reportaproblem.apple.com
If the 'report a problem' link doesn't work 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, then Purchases, Billing & Redemption
Thank you for the assist. I mistakenly clicked the item I don't want while moving my cursor to the one I did want. I then repeated the purchasing effort by clicking on the one I did want. I clicked on its price and it appeared on my iTunes music library. The one I did not want must have been clicked elsewhere because it has not appeared on my iTunes music library and it is not on my wish list and I have not been billed for it. Call it dumb luck, but I learned.
Honestly, this method of purchasing seems to have been changed since the time I loaded up my iTunes with favorite music and artists. I've never had this problem before and I started with Apple in the Apple II and Lisa days. A lot of Apple's recent changes have not, in my opinion, been useful. For example, the Calendar App for iPhone on IOS 7 is "different," but not more useful, IMHO, as well as the purchasing procedure on iTunes 11.1.3.