Best advice I could give is:
Don't do it.
Unless it is something you really need or want, the offer could never be worth the credits.
-What do you know about the charity?
-How much of what you give actually goes to help saving wildlife?
-Do they pay the people who run the charity? (If they do, not much of your donation is actually being used to help the little bunnies)
WWF(wrestling, correct?) is a multi-billion dollar business. Why do they need ANYONE to donate to that cause?
The charity is probably as fake as the wrestling.
If you cancel before donating any money at all, they will probably attempt to take back any credits. Do you blame them? Would you blame them for attaching future credits after you scam them? That's like bouncing a check.