Regarding the negative balance issue: There wasn't enough information provided to determine why there was a negative balance. But I suppose you could get a negative balance if you:
1. Got Greenpoints through purchases
2. Redeemed the Greenpoints, and
3. Returned the purchased items.

BTW, I checked my own records about the top S.P.A.M. complaint - posting of miles. On this issue, Grennpoints has delivered. I usually receive certificates within a week and the miles usually post within 15 days of mailing to airlines.