Wow. Sorry you're going through that. Personally, I would have left the store with the lens in the box still on their counter, and a firm statement: "You have seven days to resolve this and refund my money. On day 8, I'm calling my credit card for a chargeback, stating that I returned it to you in exactly the same condition it was when purchased (defective), and you've failed to honor the manufacturer's guarantee and their own guarantee."