Transaction over charged where its app**** as free

hi guys, did a transaction in august to pay for ticket using master card and on the website its clearly mentioned paying with mastercard is free, thats why we used. but eventually nedbank charged more than a 100 rands for the transaction due to that the balance went to low then one of the debit order missed that caused another 90 bucks or so, i would like to know how the hell nedbank can charge me so much where it stated as free, would have been happy if it was 10 bucks or so but i am shocked when i looked at the statement that what has been done, i need my money back for the foolish mistake that you guys did to me.