(attempted) Team killer self defence and I get banned ?!

iScending: No, you were not innocent, you killed a team member. This is never accepted and we would never overturn a ban applied by the automated team kill system. If someone acts as you just described use the in-game report tool (right click > select the appropriate option) and then let it be. If he damages you then this is registered with the automated system and he will eventually get banned for a period of time.