Q: Brought gems in clash of clans and got charged but never got the gems, what do i do?

If you haven't received the item then try the 'report a problem' page to contact iTunes Support : 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

The best thing to do is to contact the developer as they are the ones who can send the content back to you. iTunes can only refund, but refunds are never guaranteed as all sales are final per the iTunes terms and conditions.

Clash of clans is supercell.com or you can report it through the game itself in the settings of the game.