clicks website stock not true reflection, now costing me money.

I placed an online order this morning. I ordered items that was on the buy 3 and pay for 2 special as I need 3 of each for gifts. I get an email from clicks later saying that they dont have an item in stock and have credited me a percentage of what that item cost. In the meantime I now have to go back to clicks to buy a replacement and outlay money now for that item because they did not update their website. If they had that item as out of stock in the first place like they should have then I would have gone into the store and gotten the special there but now I have lost out on the special and have to outlay money.

When I phoned them and asked to cancel my order and refund me they said that they cant and only when the order is in store I have to go there and exchange the items.