Terrible service for online purchase,

I bought items form your online sale- added my items paid. After would to see that 1 of the items was left out. I therefore not getting my full value of 50% discount. I went back to my basket and it still shows the same items i already just paid for. (a glitch on the online system) This could be to get more order at full value?? I dont know!! I immediately called the call center for assistance in adding the 1 item (which they have stock off). I spoke to a Nicole 10.21am, gave her the details and was told she is unable to assist. I must either place another order or wait 20 days for my refund. Or take the items back to the store and get a refund. Her manager is unavailable and she spoke to a colleague, and that person advised her she cannot add this item to order, the only options are to wait get a refund and purchase it again. I then asked her to send me an email so if i placed another order ( as suggested) i could get my full refund for my items and i get the response of OH MY GOD... Are you doing me a favor by assisting your clients? You have terrible customer service. I would also like to know why i cant add to an order that was placed minutes before... Very disappointing service received. Please advise if this can be sorted (my item added to my order)