"¿Ustedes no llaman antes?"
The "correct" answer: "you do not call before?" is not grammatically correct english. It should be: "You did not call before?"
I'm not an English native speaker, but I think translating this sentence to the past tense (You did not call before?) would change its meaning here (I think the present tense says something about the general case, and the past about a specific case). Example with present tense: Person A: I always need to wait for hours when I am going to the doctor. Person B: Don't you call before(hand) [...to get an appointment]?
You are right. It would change the meaning and that is why it would be marked incorrect if used.
I think it is perfectly ok sentence. It just sounds a bit strange outside of any context.
That's ridiculous. This sentence is clearly in present tense, and changing it to past tense changes the entire meaning and therefore is NOT a correct translation
How about an incredulous question " You guys are not calling (going to call) beforehand? Present tense has about 8 translations into English. I call, I am calling, I do call, Am I calling? Do I call? Even "I will call" is something like esta noche is part of the sentence,