How would you handle this grocery store incident?

so my wife and I go grocery shopping this weekend and when it is all said and done we have about 20 items. We get to the automated check-out line, which is awesome, we are very quick when we check ourselves out... wait a few minutes till one opens up, then scan everything, bag everything and go to pay. This is where the problem is, I swipe my credit card and we get an error message, I flag down the employee to help us out and she comes over and says, "oh, our system is down right now, we are only accepting cash" then another clerk turns around to say "yah, we can't take credit cards, we're only accepting cash" like we were supposed to know this. Needless to say, we're kinda pissed because we just spent 45 minutes shopping and now can't pay for our groceries, so we walk out leaving all of our groceries right where they were. As we walk out we look for signs telling us of this problem, none to be found. What would you have done in that situation? It's not like I was about to go and put all of the food back in the aisle it was supposed to be in.

TLDR - their system was down, we couldn't use our credit card, we left all of our groceries in the check-out lane and left the store.