I wanted to follow up. Tapjoy relented and awarded me 820 credits as a "One Time Courtesy".
Signed... Squeaky Wheel Greased
Glad to hear it worked out for you!
I got the same thing not long ago. I completed a few offers initially just fine and got my credits. Then I completed an offer, got denied credits for the same excuse they gave you. I explained that I downloaded through the in-game offer wall (which took me to Google Play to do the actual install). Asked what I was doing wrong and what exactly the proper procedure was. They came back a few days later and gave me the "One Time Exception" and awarded credits.
So I got the credits for that offer, then the next went through just fine also. Then all of a sudden the next 3 I tried I got denied for the same reason again. At this point I reset my Ad ID as suggested by several older posts on here. I didn't get credit for that one either. I finally got fed up and wrote them a politely worded email, and they explained they couldn't tie my "new" Ad ID back to my account. I then admitted to resetting my Ad ID and gave them both the previous and current ID with screenshots. I told them that at the time I didn't realize that it was against their Policy to reset ID, and I was only trying to earn credits legitimately, not scam anyone by doing the same offers over and over. I never heard back from them, but the next offer I tried worked just perfectly, so go figure. Will be interesting to see how the next one I try goes.
My personal advice to others having issues - stay on them about it, but do so politely and have some evidence to back you (screenshots are always a plus). The CS agents I've dealt with actually do seem friendly and want to help, but they aren't going to respond well to threats and abusive language. I would also recommend against resetting your Ad ID unless as a last resort after trying to work things out through the normal escalation process. (It is against their T&Cs, and technically they could ban you for it - and if you do try it and get caught, best to confess up to it right away and explain why you did). Also be aware that if you have several "games/apps" downloaded that you are working on completing and you then reset your ID, you will lose all progress for those games and they will be completely wiped from your offer wall.