Purchasing shoes

I walked into this store and got these shoes. I recon the shoes are good and i am told by the consultant if leave the store with these shoes I will not be able to exchange, or be refunded. I fit the shoes after the payment was made and to my surprise the shoes are big I am still at the shop as I was told if I leave the store I cannot return. I asked for the shoes to be exchanged seeing that they don't fit and I am in the store. To my surprise I am told I cannot be given an opportunity to exchange though I have not stepped out of the store. Is this by law fair on me as the consumer? what am i going to do with big shoes that costed me R200? can you pleaaasssse help me.