Listing items as in stock when they are not and then charking double shipping fees

Shocking customer service. I ordered a multi-plug that was listed as in-stock when I placed my initial order. I placed the order and paid for the order in full. Then I was told by Takealot that it was out of stock and that I needed to re-place my order and that would resolve the issue. Now, they are saying that actually then are not going to honour what you previously said and that I now need to pay an extra R100 delivery fee, when I have already paid in full in my original order. Why should I now pay an extra R100 shipping because of a Takealot issue on their side?