I think this is completely ridiculous, but just for fun...
You didn't actually purchase from Stern. They recommended you try one of their suppliers.
Good luck suing Stern. You didn't have a contract with them, sounds like you didn't get a receipt from your distributor either.
Fair that you're disappointed. Very disappointing.
Now walk away and spend your money elsewhere, or suck it up and get a Premium when they come out instead.