The warning sounds valid, as you have said you killed Ellie whilst he was handling a situation, and "abusing" another player isn't a valid reason to kill in this case, meaning you did RDM.
If what you say is true and this was your first recent warning, then the warn was not valid, however I think you may be mistaken here.
A warning, or punishment, is considered to be "recent" for 2 weeks. The "1 of 4" thing is for active warnings, which are considered on a daily basis. If you had a lot of recent punishments in the past 2 weeks, then the ban on top of the warn was valid. If you think this is not the case, then feel free to appeal the punishment here:
zarpgaming.com/index.php/forum/appeals and/or report Ellie here:
zarpgaming.com/index.php/forum/report-abuse
Ellie is a pretty experienced staff member, so I would be inclined to believe that you've just gotten confused in this situation, however I will link him this thread so he can clarify