Charged triple the amount for an item that was on sale/markdown

Good day,

I bought 6pack juices during your online special where they were going for R16.99. I bought 6x6packs and chose 4 flavors. 1 flavor was not in stock and the substituted if with another flavor where I was charged R43 for that particular flavor. What I don’t understand is why would I be charged R43 when my plan was to buy the ones on special? And if the flavor they substituted with was expensive why didn’t they chose 3 of the flavors that I chose and were available and they were already packed for me? I bought those juices because they were on sale, why would I want to pay R43 when I paid R16.99 for 5 packs already? Why did you not stipulate on Ts and Cs that substitute are charged at almost triple the amount of the sale price? I want my money back. This is ****************.

Oder no: o*** Order date: 20/09/2020