Subscribe-O-Matic group owners can unsubscribe you manually in case you can't find their kiosk anymore, just contact them in-world and ask for directions to their kiosk or request that they remove you from their group.
If they refuse, or don't have a kiosk rezzed and accessible in-world, please let us know immediately by opening a support ticket (include some basic information like the owner's avatar name or the object name that is sending your messages). We will promptly unsubscribe you and also contact the group owner to correct the situation.