s1, when I have to use black or white floss, I always use Anchor. It is much nicer to stitch with, although I love DMC. DMC black seems to be "fuzzy" to begin with and I often have to pick off tiny fuzz balls. Anchor is available here at ECS. It would certainly be worth a try. While in Europe, I stitched/embroidered with Anchor exclusively and only switched to DMC when I moved back here because of it's ready availability. Anchor is made in England or Scotland, can't remember.
Keeping your floss short also helps and try a slightly larger needle. I really, really dislike working large areas in those two colors for some reason. Good luck and let us know if you find out what the problem is. Some of us wash their fabric before using it.