Bad service

Hi i have a problem and wanna lay a complian for one of the stores in Jabulani Mall in Soweto the store is Cross Trainer. I lay byed jordan shoes for my kid and paid them up but changed the made but price was the same, problem was with size. So i went there today to change siz, 1st was told by the manager Tinsoalo that i cant as i have changed shoes before and after a long argument she sais the shoes were worn which thats not true. I ended leaving with shoes that i dont know what to do with as their small for my kid. Please help