If you have a Tapjoy offer that hasn’t paid out, just submit the ticket for the gems. In the little menu in the upper-left corner, tap the “Reward Status” menu item.
Then go to the offer that didn’t pay out. I have one of those quizzes that I finished but wasn’t credited for. If you bought something, get your email receipt in pdf or take a screen shot of it.
When you select the offer, you’ll have the choice to “Request Support” for the case. This will bring you to a form to fill out.
Upload your image proof and wait for Tapjoy to get back to you. From experience, they tend to take it on faith that you did the quizzes or something to get gems, since I’ve never had them turn one down because I didn’t finish or couldn’t prove I got 100%. I don’t know about the offers where you buy something. I’ve never done one of those and don’t think any of them are worth it.
Hope this helps.