Burger King complaint: Charged for things not ordered

We placed an order for ONE fish sandwich (no pickles or cheese and NOT a meal) and for a Double meat Cheeseburger meal with large fries and large unsweet tea.
At the window, we paid with credit card and then the young female began to hand the food and drinks through the window to us. A large Coke and a large Unsweet tea. In the bag were two complete meals with large fries. We said that we did not order that. The Fish sandwich was sandwich only. (And besides they never asked what kind of drink but simply poured a coke for the second meal nor asked what size fries and drink). When we said that we did not order that, the employee said, Well, I’ve already charged it on your card and there isn’t a manager here to change it.
She seemed to think we would just say, Okay, that’s fine. When I clearly said, NO! We will not pay for something we did not order, nor do we want! … she was surprised and didn’t seem to know what to do. We passed the food order back to her. Still surprised, she said, Just a minute. Closing the window, she went to ask what to do. Several minutes later, the window opened again, and an older female employee asked if we would accept a cash refund for the overcharge. We were happy to that.
It was a good thing that I had written down the original amount charged to our credit card and the amount of the cash refund … or else I would have had no record. Burger King in Hereford does not give receipts about 99% of the time. How are we to know if they are charging us correctly????