Unknown rule

I bought a school pants at pep gold spot but all to find out the size is big and they don't have sizes went to Chris hani mall Assisted by Khabo was told they won't refund me I have to take something else and they said it's in they policy it's the first time I hear about this it is not written in the slip so please can I get clarity of this rule that is not in they exchange policy . If we are not allowed to refund but are forced to exchange something just because they want to make sales then Pep is being unfair to us as customers