Great question — answering as the UphillTech team:
The part of your issue where you said "One fell through and the other just spins with the screw." tells me the hole is probably too big. Did you use the recommended drill bit size to make the first hole? When you drill the hole, take care to keep the drill at 90 degrees to avoid widening it bigger than the hole is supposed to be. Some of the drywall inserts want you to hammer them in, and then they bite the paper, others you use a screwdriver to tighten them in. Are you using the same screw that came with the anchor? Be sure to use the same screw meant for the anchor. Are you in an unusually humid area? Its a bit of a reach, but high humidity doesn't help. Also, is the drywall 1/4" thick?...
Full answer by noybman: https://diy.stackexchange.com/a/119684 (CC BY-SA 3.0).
Need it done for your business? UphillTech.
