Sorry to hear it and yes... it's all a bit ridiculous. However what you're saying isn't clear. You say "3.1.2, but iTunes would not let me". Do you mean you tried to install default 3.1.2 directly through Apple or that you had built a custom IPSW built via pwnage that 9.1 wouldn't let you install?
If you used Cydia you should of had your ECIDs on file and you should have been able to restore an older corresponding IPSW, at least as I understand it. Personally since 3.0 I build and save all my custom ipsw's immediately upon release of updates even if I don't install them (I have jail broken and unlocked 3.1.3 built, but am still running 3.1.2).
Yeah, I had a 3.1.2 image and attempted to install it through iTunes, and iTunes wouldn't let me.
Cydia should have my ECIDs and I suppose I will go through the process of downgrading, but I am traveling at the moment and now I am left without tethering, and can't forward my voicemails through email
That's why I am so sick of this and starting to really hate Apple's increasing obsession with locking us down.