I'm having similar issues with Trialpay. I completed an offer (Stance) last week and should have received 700 credits. I've long since received the goods from Stance and I have the original confirmation email (which fulfills all the required criteria).
I've followed the "support" link for the specific offer, filled int he required details on the TP support page, click submit and get an "Access Denied" error message. I've tried multiple times, from different browsers and still get the same error message. I've resorted to emailing TP (using the generalsupport@trialpay.com that I found in this thread) and have received no response whatsoever.
If anyone has any suggestions, I'd sure welcome the assistance!