I am really sorry that you didn't get your credits on time, but don't worry, it is not unusual to experience a slight delay between the download and the crediting.
Just be aware that the credits can be gained for apps you download for the fist time only! Some offers require more than just the download, so read carefully the instructions.
If you have followed the instructions, you can see the status of your offer : go to "Earn Credits", "Complete offers to earn free credits" and by tap the button "Support" at the footer of the page.