Do not waste your time. Nothing you say or do will matter to them, they just make decisions on their own groundless fantasies.
In my life, I've been through several dozens of interviews, but I couldn't even imagine that a company could treat its candidates in such a way.
You need to solve the technical challenge to apply. It's quite interesting, but you have to spend 8+ hours to solve "hard" question in a reasonable time (and I spent far more trying to create a great solution).
After that, I've applied online, and was contacted in a week by HR.
We arranged an short interview with HR, and, after that, we've arranged a technical interview (the questions are listed below). The interview itself was ordinary, not much different from an interview in any other company.
Two days after the technical interview, I've received a message: "we were seeking developers who are coming from a more Agile environment, and you lack experience with agile processes. You submitted a promising code solution and have good experience, yet it does not matter".
Me: "it is probably some mistake. How did you come to such a decision? We did not discuss this topic during the interview, so how did you assess my experience with Agile? And my current environment is pretty much Agile".
Them: "you were coming from waterfall type of production environment".
Me: "what made you think that I'm coming from waterfall, especially considering that we did not discuss this topic during the interview? We're as far from waterfall as possible. [then I described our process in more detail] As you can see, it's totally Agile"
Them: "we understand that you do not agree with our decision, but we trust our interviewers".
So, basically, no matter what was said on the interview, they just pull an accusation out of thin air afterwards, and no amount of reasoning or facts could challenge this accusation. I've spent a lot of time just so that they decide I'm working in waterfall model (which I don't). Having agile experience is so critical for them that it trumps all other factors; yet they don't even bother to ask about it during the interview - why bothering, if they can just invent it afterwards?