I think you would be more likely to succeed if you focused on fixing the way outcomes are determined in your casino so that they are actually provably fair.
In the mean time, you should remove any mention of your games being provably fair, since they're not.
Your issue with their provably fair implementation is that the client seed isn't used for the generation of their server secret, but is instead used to manipulate the final results. In the case of a card game, that means cutting the deck, and I see how that could be exploited. I'm not sure how that'd be implemented with their slots game though because it seems like the client seed does an unpredictable job of shuffling the reels, and same with dice. Do you have any ideas on that? (I really am just curious, not trying to defend this casino)
Anyway, this casino failed to process a withdrawal.
I think you're right about slots and dice. They're basically taking a non-provably fair random number and then shifting it by a provably fair random number. I could be missing something though, I can't find the actual code posted anywhere and I haven't really looked into their slots too much.
In the end, having a server secret is either pointless or it results in the game being
notprovably fair. I can say for sure it's making their card based games not provably fair. It really wouldn't be that difficult for whoever developed their software to simply get rid of it.