Poor Customer service

On the 24th of Dec bought takkies for my son now the size is too big. So when I went for an exchange they telling me that the box is not the one for the shoes so they can't help me, I should go back to King Williams Town where I bought the shoes to ask for the right box while on the slip it's the bar code for the shoes we were given at the shop. There is a slip and a box but if what happened for them to give me the wrong box I don't know. Mind you I was passing at KWT I'm not staying there. So I can't get the right size just because of the wrong box which was given by them. That means my money is lost because my son can't wear the shoes and the two stores (Lusikisiki and Matatiele) I went to for an exchange can't help me because of the box. Please managers solve this otherwise you'll lose customers