Pair of tekkies not the same

I bought a pair of tekkies for my son in January from Ackermans. When my son came back from college for March break, he showed me that the tekkies were actually different. The soles were different. When I approached the shop manager told me that the tekkies were already used and so could not be returned. She said I can go anywhere but no one will help me. The branch is Galleria mall in Amanzimtoti.