Terrible service

How the hell do you have something stock out and not have the website update??? I placed an order for milk at 10:34 and it accepted without any issues. I got an sms to say my order is ready for collection and when I get there the milk is not in my order. I asked the cashier and she said the milk was out of stock by 6am. So why was it still available on the website four and a half hours later??? I want no refund but the milk I ordered, thank you!