Admins at SPARTA never ban for no reason. When a group comes in and starts wreaking havoc it is the job of the admin to restore order. In chaotic situations there can be collateral damage, but thats the risk of war.
Did you PM an Admin at the Sparta web site and explain the circumstances? Did you make any effort at all other than having some mysterious 'friend' ask about the action?
Your friend asked why and was ignored.. why is that surprising? Why would an admin discuss an administrative action with anyone but the affected player? Why would you expect any admin to discuss their actions with some stranger?
You want to know why you got banned? Ask through the appropriate channels. If a mistake was made and it can be verified, then the action can be amended. Simple enough.