There is no customer list. The only thing Blizzard could do is ban anyone using the same IP address as someone on Turtle WoW. However since NAT is widespread in many countries and many people don’t have their own IPv4 address this would result in an extremely high number of false positives. Not to mention that multiple people could be sharing the same internet connection. Besides there’s no reason to do that. Someone who also plays on the official server is paying for a subscription. Banning that person now would just mean less revenue for Blizzard.