Citi Data Scientist interview questions

Got an email from HR saying they will give me a phone interview, and ask for my time availability. Then no matter how many times you replied (even after using another email and also asking my internal friend to communicate), still got totally no response. I mean, when you invited someone for something and then disappeared with no words left no matter how anxious your candidate is, that's at least not quite respectful.

I was asked about why I chose Citi. Then to explain a mathematical concept in a very simple way. Finally, some unrelated questions. It wasn't what I was looking for at all.