Unfortunately, we agreed to receive a % of credits, not $.
No we didn't. Did you understand that they could raise prices to customers by 33% and you wouldn't benefit at all? It has never explicitly stated that the % commission was based only on credits and it doesn't say that now. I very much doubt that any court would accept such an interpretation of it and I really don't understand why you are so keen to do so against your own interests.
I agree. In civilized country no court would agree to interpreting their terms in a way that would allow them to say 'hey we will pay you 30% of the purchase in credits and this credit will be worth X to you and Y to buyers'.
And yes, they were doing this in a way for years through their currency policy. I'm not sure but I guess they always had different prices for their credit packages. Anyway, the thing they did recently just clearly shows that they have decided they can abuse us through this practice as they wish. They cannot.
If they were doing this in some way for years and we were accepting it and they are just making it more blatant now, does not mean we should continue to accept it.