Refusal to exchange sale goods

On the 6th august I bought my wife a pair of size 6 shoes she normally wears however when she fitted them at home they were a size big. On Monday the 10th August I went with my wife to exchange them and they told me that they cannot exchange nor return which I find its a bad customer service especially being their loyal customer. The manager concerned and assistance told me that they do not do exchanges on sales as instructed by their superiors at the head office. I am so unhappy that their decision is unfair practice in light of the national consumer act that protects unfair treatment of consumers. I would like to request you to assist me in liaising with the shop to change this type of draconian way of doing business. I would like to exchange my wife's pair with her right size fit. their contact details are: ***, 9 Charles Crescent, Kramerville, Sandton.