As for the cause of the problem, it sounds like you might have overtightened the screws.
On my first board, I mounted the bindings using a power drill!
The disks didn't break though, because I had the drill on a really low torque setting. If you did the same and had it on a high setting, you could have overtightened them too much, which would make them much more prone to breakage.
After realizing that I could have been overtightening them, I've just been using a Dakine Torque Driver tool to mount the bindings. I can get the screws as tight as they need without overtightening them because I can feel where they stop in the threads.
So if you did
use a drill like I once did, don't do it anymore
. Tighten them by hand instead. That's how they supposed to be tightened.
If you didn't use a power tool to mount them then I have no clue what went wrong.
Hopefully you'll contact C3 soon and get some new disks on the way. I have had a defective part once and called C3 about it on the telecommunications device. They immediately sent me a replacement in the same color absolutely free. Got here in less than a week and haven't had any problems. Love those guys.