The "i" in this transcription was pronounced the same way your "ee" is. English has a number of ways of writing this sound, though maybe not as many as Modern Greek. If we are translating a Greek word into English, though, maybe we should use words that can be found in an English dictionary. Chi will likely be found with this meaning, but I doubt hee will.
We can't see any of the exercises learners do so it's hard to help. But in this case, it seems the sentence was in Greek so I'm assuming you should have translated it to English...unless it was a listening exercise. As I said since we can't see what it was we can't do much. Next time send a screenshot.
Actually, the exercise was, "Write in Greek what you hear". The audio was, "Το γράμμα Χ". I wrote that. However, it is incorrect, the correct answer being, "Το γράμμα Χι".
Is this just a computer program being perverse, or am I not understanding something? And, a screen shot might not help much, as you wouldn't hear the audio.
Ok, this is what seems to have happened. Both "Το γράμμα Χι" and "Το γράμμα Χ" along with some others are correct but on the listening exercises, only one can be accepted. We'll remove this sentence as a Listening exercise, to avoid any further mix ups. We appreciate your bringing it to our attention.
Here are some links to familiarize you with the Greek alphabet. You may find these a more expedient way to move on to more interesting skills, and you can always return to the first skill for review.
HINTS ON HOW TO LEARN THE MODERN GREEK ALPHABET
The Greek alphabet, where to find the letters on your keyboard, add accents, etc.
Use this to hear native Greek pronunciation for a variety of words/phrases...
And of course the Greek Forum for a variety of links.
Don't hesitate to ask anything you need clarification with.