Jet - Refund

i bought white school shirts at jet khayelitsha mall cape town and the size i wanted to change and i asked my sister to take them back she took them with the receipt she was told they need the EFT slip since i bought with my card the wanna do a refund back to my card which i don't understand and they refused to refund those shirts i am stuck with those shirts and i understand that a refund can be done back in cash no need for card please assist as this service was very bad very bad

thank you