Hello good friends of Leafre! I've recently decided to come back to KMS after being a member of Ellinforest (which I guess shut down at some point?) for a couple of years then kinda stopping altogether for another few, though I've been having some issues coming back (I'd assume caused by my inactivity)
I have 3 Maple IDs created from 1 Nexon ID back in 2010 with the help of a Korean friend, though I've since lost contact with him. My main of these 3, however, seems to be hellbanned (I can't sell or drop items, etc.); I get this message on the world select screen (I can still log into all my characters, again I just can't do certain things)

I've been trying to figure this out for the past two days but haven't been able to... from what I gathered, it could be because I haven't played in so long and/or haven't transfered my old Nexon account to the new email ID thing.
I found the hellban fix guide on this site today and tried to follow that but got stuck with this error:

which I can't find any documentation on (I've tried my best to search these forums to no avail)
I'm fairly certain I'm using all the correct information (I had it written down in a .txt file), and Google translate says that the error has something to do with the ID having multiple accounts (questionable accuracy of translation).
Clicking on [아이디찾기] opens this popup:

Clicking on the phone thing prompts me to select a Korean phone carrier. Of course I have no way to verify anything this way (having fallen out of touch with my friend after he moved years ago)
Alternatively, clicking on the blue "넥슨 홈 가기" button back in the transfer page of course takes me back to the Nexon homepage.

Anyone have any ideas how to fix this or know if my whole approach is wrong? I would love to get back into the game, but would rather not lose my mains and all my equipment, money, etc.
Thanks~ ^u^