I had an issue with trialpay and still do for now, but i think i got it sorted. here's what you should do if you haven't received your credits yet.
Go to the third party offers page and in the top right hand corner you'll see the word support written in blue...press that. A page opens up showing all your tasks and purchasers completed. Find the one your looking for, to right of it on the same line it will say "contact support...press that. A page then opens that asked you to copy and paste the confirmation email and number. Fill in the date you did the task and you should get your credits with in 48 hours. I just did it today, i am hoping with the confirmation of purchase those dam credits will be secure in my credit box soon....but i am not holding my breath.