So not much we can do here on the community except to forward to one of the admins for their attention.
Good luck and hope your get this sorted.
@amandavanceISC2 Are you able to assist or forward to the appropriate department?
What was the final result of this? @Pronto, did you manage to reschedule the exam, or else get the refund?
You said the system didn't let you cancel on account of a credit card found to be invalid --- from their perspective, you might have to sort that part out with the bank.
(Do keep in mind that it will all depend on their policy; ideally, you'll also want to facilitate proof that you did try but were unable to reach them)
While I'm not in the same soup, I can sympathize. Few days ago, I attempted to get them on chat to clarify something --- after waiting for at least 30 minutes, the 1st agent that I finally got ended up disappearing & I had to wait for another. End result: 1 question took more than 2 hours to get answered.