CREDIT CARD NOT A DEBIT CARD

I have a Discovery Bank credit card. I purchased some goods from @home, Morningside, Sandton and returned them for credit ON 21 Decenber 2020. The credit card terminal declined my card stating with an error message "Declined". The shop assistant advised me that the card terminal is reading the card as a "Debit Card" and so they cannot process a refund with that card. My card is a credit card and would like an explanation as to why the credit could not be processed. As the tills did not have sufficient cash in them I was forced to take a "Gift Card" which I do not want. I want a full refund. Please advise.