Shop forcing their customers to pay their bank fees.

Went to buy groceries for a grocery club and had to swipe my card as the funds had been transferred into my account. I had to pay R10738. 00 and I was told that I'll be charged R100 extra for bank fees. I asked why do I have to pay for their bank fees as I have to pay for my own, I was told if I swipe for R5000 and above, I have to pay R100 bank fees. It was my first time I have to pay a shop for their bank fees. I told them that when I buy for R20k at Makro or any other shop I don't get to pay for their bank fees. I told them this is brought day light *******. I need this shop to be called to order, they are robbing their customers, why do we have to pay to buy from them? How much do they get from the R100's they demand from customers. If there are 10 clubs, they get R1000 extra. This shop has to pay back all the customers they are robbing. I'm taking this further up to the Consumer Protection. Please get the management to answer. I told them that I'll take this up.