Their support has been very responsive with me, even if it takes a second to get a reply. I cannot believe that they would not reverse this in good faith if you proceed to not utilize the credits or whatever.
If they don't address this reasonably, it will be a very bad image for their brand! It is a simple problem, and an honest mistake that functionally should cost them nothing.
My customer service experience with them has sometimes required turnaround time, but never been helpful or unreasonable.