KFC Casheir tried to **** me on Saturday

This weekend my partner and i went to KFC in the morning to get a quick meal. When we ordered, and got our food, we realised we were charged an extra burger but then the burger was not even in the bag. After approaching the cashier about it, she casually laughed it off and claimed it was a mistake. Well, mistakes do happen, but my question was if it was a genuine mistake why is it that the burger was not even made, and it didn't come to the pass to be packed with all the meals coming out. It suddenly dawned on us that this was just a plain ****, as our till slip showed something ordered, and money was deducted from our account (as we paid with a card), but the burger was not even made at the back. To me, this is the highest level of ********, and it is in such situations where people ***** money from you (albeit indirectly, as they charge you for goods you know nothing about). I would certainly like to get an explanation about such kind of behaviour. Although the manager tried to resolve the issue by refunding us, no one had a response as to where the burger was, and if it had been a genuine mistake of punching in more meals than ordered. Just blatant thieving at its highest LEVEL