One crazy chicken

So I went to El Pollo Loco, which is foreign for "Best Fast Food EVER" last night and had the most maddening experience.
So here's the drill: The wife and I both order the No. 2. That's two pieces of chicken, a side and a drink. Then we order the kids' meal for the Manster, and his comes with a drink too.
So I go to the drink machine and realize I only have two cups. I go back to the cashier, and she says:
"I didn't charge you for a drink on the third one."
I said, "But we got two combos and a kids meal. Don't they all come with drinks?"
"Yes, but I didn't charge you for it.
"Well, you don't have to charge me for it, if it's in the combo, right?"
Lady, perturbed: "It's on your receipt."
"What is?"
"Where I didn't charge you for it."
"Well, WHY didn't you? I didn't tell you I didn't want one. I wanted a drink. That's why I ordered a COMBO."
"It's on your reciept."
So I go back to the table, very flustered and more confused, and look at my receipt. Here's how it worked... the combos are $5.19, but we upgraded to the breast/wing pairing, which is now $6.19.
So the receipt goes like this:
First item: $5.19 plus $1.29 for drink. Then a coupon was apparently applied, for $.29. So I guess that makes it $6.19.
Then the kids meal, which is normal.
Then the third thing, which is $5.19, the normal price of the combo without the "upgrade" charge. So even though I ordered it, she just didn't feel like doing it. She was saving me some money, I suppose, in her demented mind.
So I go back, and debate the whole thing, then go back up to the counter to order a DRINK that I WANTED the first time. And the lady just stands there, looks right at me, and acts like she's never seen me before. "Can I help you?"
"Uhhh... yeah. I want a drink."
With tax and everything, it was $1.39, which was $.39 MORE than it would've been if I'd just GOT what I ORDERED. Not to mention the complete frustrating experience, the total confusion, and the fact that I was pissed for like 2 hours after that.
But the chicken's flesh still was tasty after the fire singed it a lot.
Thanks for your time.