English is my first language

So, Starbucks has these $()%&)&@)@&)(#&@# treat receipts where if you buy a beverage in the morning, you can come back after 2 pm and get Grande iced drink for $2. Sounds like a good deal, right?! Well, I end up drinking about 10 starbucks drinks a week now. :(

I'm ALWAYS in a state of confusion on how to order my drink after 2 pm without using 15 words to describe the drink. I want a nonfat carmel latte. Well, it HAS to be grande and it HAS to be iced (says so on the treat receipt stamp). So, do I need to even use "grande iced" or not???? Also, I always feel the need to mention the treat receipt because once I didn't and they acted all out of sorts when I handed it over. I think they had to void it and redo it...... I'm too confused.

Anyways, this is my conversation today in the drive thru (Cause I'm lazy like that)
Starbucks: Welcome to starbucks. What may I get you today?
Me: I'd like to use my treat receipt to get a grande iced nonfat carmel latte.
Starbucks: I'm sorry, I can't hear you. Hold on.
Next person: What can I get for you.
Me: I'd like to use my treat receipt to get a grande iced nonfat carmel latte.
New guy: Do you want a carmel macciato? (no, had one this am)
Me: No thank you. I'd like to use my treat receipt to get a grande iced nonfat carmel latte.
New guy: An iced latte? Ok. It has to be a grande, is that ok??
Me: ????????? didn't I say that?!?!?!?!  "Yes please"
New guy: So, a grande iced carmel latte?
Me: Yes. Can you make it non fat please?
New guy: Oh, sure. (didn't he hear me?!?!?!?!)
I get to the window....my total is $4.xx. Sigh.
I hand over my treat receipt, that I have now mentioned 3 times. when they see it, I obviously have caused a huge problem. I am starting to view them like Hobby Lobby. They had to redo everything and I could tell I am not their favorite person at the moment.
Any suggestions???