Why not "call it"? I'm constantly losing hearts over the apparent ambiguity of "lo and la" here.
An "it" that can be called would be a robot. Considering that Duo is a robot I think it should be accepted ;) But should not also "her" be allowed? I just lost a heart on that.
You could call a number you didn't recognise, or call the speaking clock, it doesn't really matter- if it's a possible translation, however unlikely, it should really be included. :/ If it was "call her", however, I think it would probably be "(Io) la chiamero", rather than "lo". (:
Because "gli" is for indirect objects, and "him" is a direct object in this sentence.
I have just had 'I am going to call him' marked wrong and the correct translation said 'I am going to call him tomorrow' - I don't understand where tomorrow is in that sentence.
Should be I shall call him. I don't understand why they get this wrong every time.
While 'shall' should be accepted as well, 'will' is also acceptable because it's more common in many places. http://grammar-monster.com/easily_confused/shall_will.htm - especially if it is important that the call happen.
Presumably they don't have enough people to sort it out. Even a cursory glance at basic grammar books will show you that "I shall call him" is a more "correct" form, even if "I will call him" has become common in everyday use, and not just saved for sentences where you want to express determination.