Explain on producing an ID when purchasing using a credit card.

I went to Cambride Umngeni in Durban.I pushed my trolley to the till and when it was paying time i took my credit card from my wallet and the cashier wanted me to produce an ID, which i didnt have and i was told i am cant pay using my credit card.I am not a South African I am a Zimbabwean therefore walking around with my passport is a risk if it gets lost to get a new one its about US$318.There are notices in the shop but they are not clear and they are written in IsiZulu which i do not understand.Funny enough I was allowed to use my debit card without an ID. I was embarrassed today.