Hey, for Kati is not listening we would use Kati nem hallgat. As you can tell, the verb hallgat includes hall. Though people don't necessarily think of it that way these days, hallgat very literally would mean something like hear again and again. But that's just a side note.
Wiktionary summarises the differences between hear and listen like this:
“To hear represents automatic, unconscious, or passive perception of sound, while listen generally represents intentional, conscious, or purposeful use of the sense of hearing.” (from: https://en.wiktionary.org/wiki/listen#English)
The same holds for Hungarian, where hall corresponds to hear and hallgat to listen. For example, when you are walking down the street and you hear music coming from a bar, you'd use hall. But when you stop and listen to it consciously, you'd use hallgat.
Thanks! I recognize the difference between the two terms, I just don't use the phrase that someone "hears" very often and automatically substituted the more common expression of "someone is listening." But your explanation was very useful for remembering both and their Hungarian terms.