No stock online... again

On 3 separate orders that were placed online they refunded me because they don’t have the items. There is nothing more frustrating than placing orders online, and was the case with Total Sport to add extra items to qualify for door to door delivery and then what happens. The items you actually wanted they don’t have stock and refund you. Surely there is software that depletes stick levels when someone checks out. Or maybe the problem is that you source the stock from different stores. Either way I think it’s unacceptable