Double charged

While paying with my virtual card at Ok Food in Vanderbijlpark the card machine went off line. Although I already received an sms from my bank that the transaction was successful, the cashier insisted I need to pay again. She promised that Ok will refund me if I was double charged. My bank statement shows both transactions. The manager and staff explained to me that it happens to many customers and it is my problem and I should contact my bank to fix the situation. Although I was very upset, none offer an apology or assistance. Should I be liable for card machines which go offline? Apparently I and many other customers should which is unacceptable! Very disappointed!!! And still not refunded…