If you completed an offer via Trialpay and have not received your gems yet, please go to this link: https://www.facebook.com/help/?page=149756025094082
There are two options on that page. One for completing offers for Facebook Credits and one for completing offers for in-app credits. If you chose to complete the offer to receive Gems for Dungeon Rampage, you would choose the second one labeled, "I completed an offer/promotion with TrialPay to earn an in-app currency, but I didn't receive it".
The TrialPay team should be able to process your request internally.
If you have already contacted the TrialPay team and are still experiencing issues receiving your gems please create a new support ticket to us.