I know I said that they can't be killed, but maybe, as they breed in despair, you could feed it so much happiness that it exploded from joy and all the souls were released
Hmmmm, cheering charms could do it! Thanks
I could change it so the ministry is experimenting on ways to get rid of them, since they don't control Azkaban anymore.

Flamethrowers. Everything is better with flamethrowers. That's the way to go.
I have to agree! Incendio or lynx and a lighter? lol

Thanks for the link, it's really helpful