How could they do this to customers

I went to cross trainers in forest hill and bought a pair of air max in December!so when I got home my little brother tried them on then he was walking with them in the house that's when he realised that they are tight so we kept them in there box until I was able to take them back to the store I bought them for exchange then they tell me that they can't exchange them because they are dirty so what must I do with the small shoes that doesn't fit anyone and that cost me R1199.95