Selling things that are not available

I opened the account online and it was approved. Ordered items online and paid with the account and got the order number. Two days later I got the email and sms to advise that the items I ordered are not available I will be credited. I called the call centre and was told that I have to call first to confirm if the item is available or not, according to their shopping online system the items are available. I always buy online and never experienced such incompetence. Only shoes are available, what will I do with those shoes without the dress. I have to spend airtime to call and check if items are available and also pay for the items I want. Truworths should always update their system, if item is not available it must also show on the system to avoid inconvenience.