Let's face it, there are just some knots that simply cannot be saved. As a last resort, the hair should be removed to prevent further damage and more hair from tangling with the already non-salvageable hair. In an effort to save whatever hair you can, try using this recommended technique from Hairfinder.com:
Take the matted hair in hand and with the point of your scissors facing the http://www.kiwibox.com/sofunnaturalhai/blog scalp and sever the matted hair halfway. Add a slippery conditioner to the ends and allow to http://simplehairtrticksnow41.jigsy.com penetrate for several minutes.
Using a wide toothed comb, work through the matted hair in an attempt to loosen any salvageable hair. If this method does not work then you may want to consider removing the matted section all together.