Over promise under deliver

I mistakenly opted for a collection service from Makro Silverton for a very large order (short of R20k) and then realised it was a mistake. I called them twice, both times they assured me they will deliver the same or next day. Unfortunately, in spite of the calls and my request they still did not change my order to delivery. Although the initial mistake was made by myself, I feel that they couldve just declined to deliver and not let me think it will be delivered when in fact, it will not. I am not left with no stock and possibly having to cancel the order and shop elsewhere because of their poor communication and false promises,