I'm pretty sure Armor Games doesn't deal with this.
There's no reason you shouldn't have $7 remaining. It's no different from other pre-paid cards. If you used your card to buy something for $8 in Dino Storm, you should still have $7 left for something else in Dino Storm.
What Gantic mentioned is correct, I too believe you should have access to the remaining balance on your Ultimate Game Card. Maybe you should try to have a look at the Dino Storm Forum for bugs and reports. You can ask for support on your problem in the Dino Storm Support section and they can help you further, as this is not something ArmorGames can help you with. ArmorGames is a host for this game and isn't able to help solve in-game problems like this one... I hope you can get this solved, but we are not able to from our end. =)