What exactly happened? evolve doesn't cost diamonds.
Where did you receive a response from "Gree" saying they don't believe you? You'd be the first user I ever met with a personalized response from Gree. Do you mean the in-game Customer Service? Did they check your account and either say nothing was missing, or did they give you some explanation of what the system says you spent it on? Details might help me help you with how to respond.
Which bug are you referring to? A little help here. There are alot of bugs in the game, I'm well aware of that. I have yet to encounter or even hear of this issue. (Doesn't mean it's not possible, but it new if it is.)
Have you tried exiting the game and then logging back in?