Can't hear chords in songs

HELP please! In Level-up I successfully passed World 1 all 2-star levels, and can hear chords ok (although often have trouble with IV and V), but when I try to do the bonus level, where there are actual songs, I am completely stuck. So 2-star bonus level of World 1 is completely impassable for me right now, I just can’t hear the chords. At all. What can I do???