How do I find out what my account was banned for?

[ragermann]

I played BO2 quietly at night, rebooted my PC and went away for five minutes to smoke, came back and saw that my account was blocked for no reason...

[WolflexZ]

You probably violated and trigger the anticheat. Then tried to bypass it, which increased your ban length.
https://plutonium.pw/docs/anticheat/