Refund Refused

I had bought a nike takkie from sportzlink linksfield terrace on the 31 December 2017, after using the shoe for a couple hours it started to open up, I then returned the shoe within the 7 day period and after a couple days they told me i'm allowed an exchange yet they could not replace me with the shoe i got in the first place.If you look at the consumer protection act i am allowed a refund at this stage yet she insisted not to give me one and says its against company policy!