Poor customer service

Today I was at Checkers Hyper Menlyn Shopping mall. I purchased groceries and paid with my gift voucher. I swiped the gift card and for some reason there was an error. The cashier was so rude asking do I have money on the card, I told her there should be enough money for my purchase. With an attitude she tells me the system is giving her an error 501 that means there are insufficient funds on the card. I told her there must be something wrong with your system, she rep****: the system can't lie. She was in hurry to know off and did not care about the customer. Next moment she took the trolley with my groceries to the office with the slip after I have asked her to check the card again. A new cashier came to the till, I asked her to assist me. When she checked the amount on the system it was less than what the first (rude) cashier told. I swiped the card and the transaction was successful. No supervisor or manager offered any assistance. I'm do disappointed in the poor service I received today. Stop treating people of color as if we are not use to give cards. If it was a white person he/she would have gotten excellent service. Educate your staff on give vouchers /cards. Please send them for customer service training.