Bad Customer Service

I was paying for my groceries and asked the cashier to check my balance on my pick n pay gift card which I have been loading with cash. She confirmed I had R281.00. My shopping was just over R400 so I asked her to use the R280 and I will pay the difference in cash. The R280 declined. She told me the gift card is offline. I asked so now what. She called the till supervisor and explained the situation. I told her I have no other cash. She then told me if I have no other means of paying then they can't help me. She proceeded to void my transaction. Not even an apology, the attitude this was all done with is shocking. It's not like I won the gift card. I actually put my hard earned cash for them not even to show empathy and just tell me I can leave the groceries if I have no other means to pay. As if it's my fault their gift cards are offline. I was so angry and embarrassed. I told her I'll transfer money on my cellphone banking quickly from my savings account and pay. She then said they'll help other people so long while I'm doing that. Terrible experience from a Supermarket i've supported for so many years.