You were banned on March 20th by Blackphoenix13:
You were x-raying at coordinates: 1181 26 -782, mining without torches and directly to gold ore.
Length: Permanent
So it appears you were caught using a mod that is not allowed on this server.
If you have truly been out of town, then it seems your account has been compromised. I suggest changing your password and replying to this thread when you have done so. When you have, wait until an admin/operator contacts you to discuss the situation.