Exchange of shoes

Was at woolworths edit mall of Tembisa exchanging shoes that were small but still had the original tag, Ncumisa the manager refused to exchange for me, her reason was that the color I was exchanging they do not have in her store and that small stores are not allowed to to an exchange on items they do not have in store. . Therefore she cannot process the exchange. I failed to understand cause I wasn't doing a refund but an exchange.