I believe the reason why your accounts were banned is because you bought the "Rose of Hod" of the player who sell them in kiosk.

The GM stated:
Quote Originally Posted by Rapturous View Post
Notice regarding Golden Dragon and Rose of Hod Events:

These event items are untradeable by design and if you see any of them being sold in a sellers kiosk it is a result of illegal abuse. Please do not purchase these items as the sellers will be banned and items will be removed from the game. We will not refund cegel for any items purchased after this announcement has been made. Thank you!

The Seal Online Team
So that's that. Do not buy the "untradeable" item if you see them in the town if you don't want to get banned.