Does spawn prot even work?

That's different.
Spawn protection = 3 seconds of protection when you spawn.
However, combat still works, if you get hit by a bullet and log off, you get pvp log. People can kill you then. That's logger protection.

 

Spawn protection only last for a couple of seconds. If you were tagged into combat and logged, your character would become a "PvP logger". You most likely combat-logged without realising.

 

See above. You probably got hit without knowing it, and voila! A PvP logger entity, carrying all your stuff. It didn't even damage the diamond.
Next time, wait for a while before logging off, maybe you could hide/shift someone out of the way, THEN log off.

 

You should have typed in the command that would have maked you not in combat then log off

 

What command does that?
If you mean /ct, that only tell you if you are in combat or not. If that was a command, people would get in a fight, use /ct, then log off to avoid death.

 

As said above several times, you most likely combat logged without realizing. At the same time, if you log in and log out several times rather quickly, it would kill you as well. Refrain from doing these things and you won't die. /ct to see if you are in combat, then you can log out.

 

Yeah that's the one, I completely forgot the command for a sec