Tell us and stop there — do not open it. A slab that arrives compromised is our problem, not yours: we refund in full including shipping, or source the same card at the same grade if you would rather have the card.
A label that does not match its contents is a serious matter and we treat it that way. We report it to the grader with the certification number, because a mismatch is something the grading company needs to know about too.