Maybe the Instantkill is the main reason as to why your account was banned. That's sad man
It's not the instant kill, it's the no zombie attack.
Because zombies are completely clientside, their dmg, their hp, their attacks.
BUT the client sends magic packets (those are the same packets that cause sync/de-sync problems), and those most likely contain information about zombies' hits not registering.
it is more likely that you were standing still when fighting bosses or grinding, that may have caused the ban, also if you have been using exp hack, that may be caused it as well....
i never use exp hack, and I wasn't standing, because i wait to boss to appear, kill and loot him, and went to SB to scrap that shit.
i dont know what's happen because i used to do that a lot, and never get permanent ban.. not even 24hs ban