Are you sure he doesn't have Admin privileges or access to Control Panel?
There can be a chance that he somehow stole your Password and Email and now he controls your ban list.
So I recommend you change your password on your email and 
Aternos account.
Posts by Kusarek
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Hello
Aternos
FutureCraft is the official modpack of Czech YouTubers Gejmr and MenT (both 1M+ subs) on which they have played their series for four years. (from 2013 to 2017)
It would be really interesting if FutureCraft could be added back like then, a lot of players used to play a lot of FutureCraft so it would be nice to bring FutureCraft back to theAternos modpacks.
FutureCraft has a lot of interesting mods, for example, a Galacticraft which allows you to get launched into space and travel between planets like a Moon, Mars, Venus, and more...
Thank you for reading and have a nice day!