That would be, for me, like debating a creationist when they say "Show me proof that God does not excist". I simply will not enduldge in it, out of intellectual honesty.

However, we can have a look at one of their live appearences:

https://www.youtube.com/watch?v=wEpqxlN61Ag

Obviously, there is no gothic rocking going on in this live appearence. It is undeniably a metal show, the muscicians are undeniably metal heads, they undeniably riff like a metal band and they undeniably pose with their guitars like metal heads. You don't have to be a journalist to see this, you only need to be able to know the difference between what gothic rock sounds like and what metal sounds like. A source claiming that Evanescence is a gothic rock act is, really, not a realiable source.