Welcome to my world! I have the same problem every day, but with classes of up to 35 unmotivated primary aged students.
I figured out some time ago that to provide the motivation, a different approach- rather than the typical ESL protocol- was needed. So I came up with a whole load of hands-on activities and experiments to help my students become engrossed with the subject (by 'subject' I mean ESL, but to the outsider looking in on my classes, they would think I was teaching just about every other subject besides ESL!). You'll find, if you use this approach, that one day something you do will hit the 'spot', even for the most stubborn student. And from there on in, it will be coasting all the way.