Ha, good that this thread came up again. It reminded me of deleting my webtoons account.
I had huge issues with logging in twice, in the past. Then I stop publishing there because of the senseless censorship, but.. when I came to delete my series, I could not log in AGAIN!
So I tried again today after reading this thread and after a little bit of insistence I got in, deleted everything. Thanks for the peace of mind.