Bad bad bad bad bad service

I bought a babies formula Nido for R269. 99 and on the shelf is priced R249 that's the price I always buy with so the cashier by the name of Mavis Sekhul said to me I can't buy with 249.00 because I don't have extra savings card then I said to her you did not ask for the card and I have it instead of her standing up she referenced me to kios telling me to go there and ask for refund and I should tell them that I don't have a card of which I have so me as I client must I go there and cover her mess because she failed to ask a simple question and I want my refund because as furious as I was I left the store. She gave me a kaak service or is it because she undermid me? I want a formal apology and my change... I don't know how are they going to sort it out because should I drive there I need my petrol as well because it's not my mistake it's your lazy cashier....