Return full amount

I bought my kids clothes for December and when I got home in Limpopo they had duplicates,I couldn't return them in any of the ackermans stores back there because I left the receipts in JHB ,I then came back last month to exchange where I bought them in Rosebank mall and they told me they'll give me with the reduced price then cause that's their policy but I still don't get it I paid full price cash and I had the receipt ,this is a daily *******,I'm just pleading with the management for the full amount cause I paid cash I don't owe them anything