AMC Theatres review: incorrect billing for food

I have the ACM Theatre app on my phone. I went to the AMC Theatre in Menlo Park, NJ to watch a movie today. As soon as I was in the proximity of the theatre, a notification from the AMC app popped-up on my phone. It said I had a $5 reward.
I ordered for food in the dine-in theatre, and showed them the reward. The server took the phone and punched in numbers from the reward into his order taking device.
I paid for the remaining amount of the bill.
On coming home, I checked the receipt and realized that the $5 reward wasn't applied on the order at all. And now my AMC account does not have the $5 reward either.
I chatted with their customer service and called AMC as well, but none of them made it right.
They're asking me to go to the theatre again and talk to someone there to resolve my issue.
It surprising that a company so big could nickle and dime their customers like this.