You were banned for resetting your challenges so you could get the credits over and over again. That isn't 'unfair,' that's network manipulation. Hundreds of people have appealed their bans and there has yet to be a single case where the ban was given unfairly. If you feel it was, however, click here, read the Employee's post. If you are innocent, post in the thread saying so and if you're correct, then your credits, rank, and armor will all be restored to you. If you're lying, however (and don't think you can fool Bungie- they can tell), your ban will be doubled.
Good luck.
[Edited on 11.03.2010 3:33 PM PDT]