Offers you find in the Earn Free Gems section come from Tapjoy, a 3rd party offer provider.

For some of the larger Tapjoy promotions it can take some time to get the confirmation but sometimes the service just gets stuck. You can contact TapJoy directly and they should be able to help. 

To contact Tapjoy, go to the Free Gems screen and tap the three white horizontal lines in the top left corner of the Tapjoy Offerwall to open the menu. Then tap on Reward Status, then the Not Rewarded tab to view details about the status of any promotions in which you were not rewarded. If you are presented with the option to contact Tapjoy here, you can fill out a form that will go to TapJoy so they can investigate further. Please be advised that sending more than one email without a reply may result in a longer wait time. If your email address is not accepted you can contact tapjoy via the website here: http://tapjoy.force.com/