Merchant refused to swipe my debit card for R15

I went to the BODY FUEL EXPRESS store in CENTURION to purchase a slushee drink for my niece. The sales lady rudely declined my debit card as payment for the slushee saying that she can not swipe my card for the amount of R15 as her bank charges will be half of that amount, and the sale therefore not profitable for her. I explained to her that merchants are not allowed to decline payment via debit or credit card just because of bank charges. I know this is I work for a Bank. She said that it’s her decision to make and refused to proceed with the sale. I left the store without the slushee, much to my niece’s disappointment. Kindly advise your merchant that such behavior is unacceptable and tarnishes your Bank’s reputation as being perceived as charging excessive fees thereby preventing her from swiping cards for sales below a certain value. Kindly provide feedback to me on the status of my complaint. Thank you kindly.