No delivery of online order

I have recently made the terrible mistake of buying groceries online at Pick n Pay. I have ordered multiple stuff from their online store including specials that was only valid for that one day. After going through checkout (eventually, as the checkout had technical difficulties), I had to book a delivery date and time...which is only 4 days later....no problem with that, problem is, receiving the order a bunch of stuff wasn't delivered. I phoned customer service to enquire why it wasn't delivered, also noticing that most of the undelivered stock was part of that one day special. Customer service informed me that it wasn't delivered because they were out of stock...please note that the products ordered wasn't fresh goods that can only be packed day to day. When I placed my order 4 days earlier, I expected from this ONLINE shop to keep out the items ordered. This was not done! Unacceptable from an ONLINE SHOP. Thus everytime you order something online from them, you gamble and hope and pray that the item/s reaches you, beacause they don't inform you that the product is out of stock. Unacceptable. I am outraged as I needed the items and expected an ONLINE SHOP to deliver!!!