Hello,
They can manage to make the links between your old and new accounts, you do not use the same browser? never same ip (you told that you use VPN but you use also to create account?)? Also, try download again the Wow client for a new account. How many hours per day you bot? You have try to use different fightclasses/plugins/profiles?
They do not necessarily ban when they catch you, some wait and ban several users at the same time.