Why allow purchase if no stock!?

I made a purchase online and selected the Fourways branch for in store pickup of a heater as mine packed in yesterday. The site allowed the purchase with no warning of stock out. I then receive an email saying there is no stock at the branch and I need to wait at least 2 days!! Does winter go on hold for 2 days while I wait for stock? I would have expected Hirsch's to source the heater and deliver asap due to their fault in this instance.