Selling online items they don't have stock of

I've ordered a tablet on the 29th Feb online, with the option to collect from the Cape Gate store.<br> <br> They called me yesterday (after asking what's happening with my order) to offer me a discount on another tablet. If I ordered an item for certain price, I EXPECT to pay just that.<br> <br> I've just started to change my perception about the JD group's customer service after receiving EXCEPTIONALLY good service from the Canal Walk store (who was also out of stock of the same tablet, but immediately, without any hesitation upgraded me to the next available tablet for free), and Hi-Fi corp Cape Gate.