Windows Smartphone for ONLY R499

in an online sale in step 3 of the checkout procedure (of which I did a screen clip) it gave the price of the combo R548 but when I clicked on step 4 which is checkout and add to cart the price changed which I only noticed afterwards.( to R949) In our communications afterwards they said I where to late for the promotion. I still can't understand that quoted price differs from invoice I wonder how many customers where deceived this way.