That’s actually not true. According to Theme Forest’s policy, you can approve a refund. Seeing as though your theme does not cover the basic functionality of allowing users to add more than 12 photos to one of its primary features, I believe this warrants a refund. I also recommend that you update the description fo the theme on Theme Forest.
Do you have an idea of timeframe? I appreciate you forwarding it on to your developer, but the limitation cannot be fixed within the next week or two, I will need to find an alternate theme.