Upset customer

So now Ackermans wants to rob me of my hard earned money. So I went to Ackermans bought school items worth R2549,20 which all qualify under the R650 promotion. According to my understanding I was discounted for items worth R1950 which is 3 R650's. Which means that I was not discounted for R599,20 as that amount does not meet the promo requirements. I than send back shoes worth R319,99 now they say they are going to take away R150 cause I was not discounted.my question is why don't use the R599,20 which did qualify for the promo to take away the money for the school shoes. I've spoken to shop manager Siboniso and called customer care spoke to Yolanda who ended up dropping my call cause she didn't want to get her team leader and have not received a valid explanation.