Just to add in, I have seen posts about this issue numerous times. And other users are kind enough to give solutions, however none of these solutions work. Please be aware that those who have this issue, we know what a "repeat one" means.
Ever since I could remember the Music App on the iOS always only looped the current song when the song ends on its own and replays. HOWEVER, hitting the forward button just replays the current song over and over again. If we turn off repeat, the current song doesnt loop and yes it will go to the next track. But that's not what we are talking about!
Also, changing the Up Next doesn't do anything. It keeps adding the same song over and over again.