Misleading promotion & disappointing service

I ordered a laptop online from Incredible and, after tracking the delivery myself, collected it from my selected store. The laptop box had a sticker clearly stating: “Remember your FREE Incredible gaming backpack. T&Cs apply.” I therefore stopped looking for a backpack and contacted Incredible to find out how to claim it. I was then told the sticker was “included in error.” If this was an internal error, why should the customer bear the consequences? The promotion was physically displayed on the product packaging, so I had every reason to believe it app**** to my purchase.