Player was out of zone on an alt but logged in and took my camp

[Malk]

AFAIK the only rule that applies in a somewhat similar case is that if you are camping several mobs (distant, but in the same zone) and someone comes in and wants a camp, he/they have to inform you first and you have to choose the camp you keep.

I'm pretty sure this doesn't apply to OP's situation, where logging out the main is an auto-concede of the camp. OP should probably escalate this to staff.