When I translate "Who did Mario call?" and "Who called Mario?" using Google Translate I get "Chi ha chiamato Mario" for both cases. So is the Italian question ambiguous in this sense?
What if I absolutely need to, to save my life, make the other person understand that I mean to ask "who called Mario?" and not "who did Mario call?" (or the other way around)? I'm asking this because I was pretty much in this situation during my Italian lessons trying to ask this very question, in Italian, to my Italian teacher, but I couldn't find a way to make the distinction, so I kept repeating "Chi ha chiamato Mario" trying to make emphasis on different words, but apparently I didn't manage get my point across so I gave up and decided to ask here.
The weird thing is that you can make the distinction in first person: "Chi ti ha chiamato?" vs "Chi hai chiamato?" so I guess it should be possible to also make it on third person if you absolutely have to.