That isn't a packaging QC problem, that is a person dropping the case and the can popping the top on it. Then again since it is a lowcarb/ sugerfree it probably got too cold and the ice popped the top on it.
You should have taken the case back to costco, (I am sure they would have replaced the whole thing much like walmart exchanges stuff all the time) rather than call Monster about it. If you insist on calling Monster do as Zabe said , ask for a supervisor, tell him your story and the name of who you spoke with and on what day/time etc. and more than likely he will at least send you some coupons for some product.
If what you did yesterday still looks big, you haven't done much today.