Impossible to change order delivery method

I have been a loyal Takealot.com customer for years. Today I placed an order for items that I need delivered tomorrow. At checkout I opted for the "next day" delivery option which costs R100. After making the payment I received the order confirmation email stating delivery will be next week Saturday. When I enquire about this, the response from the supplier representative is an unsympathetic "you should have checked the delivery date before completing the order placement". What kind of nonsense is this? Why would I pay R100 for delivery 7 days from ordering when the delivery on Tuesday the 18th would have been free of charge? How is it not possible to change the delivery method when the order has not even been prepared. This is such horrible service. If I could give a negative rating, I would.