I can very well feel your disturbance about getting fired. I can very much imagine I'd feel the same (and hate myself for feeling so strongly about how some bunch of a****les acted).

I haven't been through this yet (thankfully), but I did heard that much of it is normal:

• telling you in the latest moment possible, for fear you might do some damage if you continued working after knowing you are being sacked
• Not being up to any discussions; once the big boss tells you about it, the decision has been made, irreversibly. No amount of reasoning will change it.
• It happens that people get fired without any fault of their own; in that case the reason presented to you was probably just an excuse

As a piece of encouragement, please consider that

• It wasn't the decision of the people who worked with you, but somebody else, probably for reasons completely unrelated (financial maybe, or looking for somebody to place some blame)
• The big boss who fired you was probably pretty much indifferent about you; he didn't hate you. There are good chances you'll get a good letter of reference; he doesn't gain anything from earning your (or your direct supervisor's) enmity.

I wish you the best of luck, and hope that you'll find something to do which you both like, and which can sustain you.