I ask that you please message the admins ingame or at firstname.lastname@example.org
They can give you a more thorough answer as to why you were banned as well as lift it. We do not discuss bans via forum topics. These are private matters between you and the staff.
However, from what you stated, the admin most likely saw this as "multi account" and banned. Your IP showed up for same account, multiple places. Try to avoid logging in at your friends place. Playing while right next to your friend in same room will also get you the same issue. Email the admin, make your case, and they will make a decision.