Great Vault Dispenses Incorrect Reward

Not wont. Can’t.

GMs cannot switch out rewards or fix bugs, if this is a bug and not an accident. If it was found to be a bug and a fix got implemented, you could get double the rewards (the one the GM swapped and the bug fix one) or your account could even become bugged more.

I know it is painful to not get what you were expecting, but sometimes that literally is the answer, that nothing can be done.