well shit, that sucks, what a pain in the ass

you could try to pick the lock, i imagine it wouldnt be too hard, and a locksmith should be able to pop it open pretty easily, but thats not something that you should need to do or pay to do

i would go down to sears in person, they will probably tell you to call customer service, but dont take that shit, they can call someone who can fix the problem directly, just force them to do it

other option is call your credit card company (if you ordered it with one) and cancel the payment
that should get their attention and get you your key pretty fast

regardless, good luck