Optiver Quantitative Researcher interview questions

Simply the least professional HR interview process I have ever undergone in my life. Before applying for the position, as a candidate you are supposed to solve an exercise they propose suitable for people expected to at least have a PhD in physics/mathematics (which I do). Having sent my (correct) solution, I got rejected straight away (which gave me the impression they did not even bother to open my file), but so far it was fair enough. After two weeks I was surprisingly contacted by the very same person who discarded my application in the first place saying that she was very interested in my profile but unfortunately could not open my attachments. On resending my solution, I asked her why she had initially rejected me if she had not even opened my files beforehand. No reply, no more answers, HR just disappeared. Anyway, since I happened to know someone already working there, I escalated the entire issue in order to understand what really happened and the only thing I got back was a message on my answer machine from the HR in question, mumbling my solution was incorrect (which by the way was not). Overall experience: HR do not even open the applications and just randomly select. Very unprofessional considering that on the other side there are highly educated and experienced people with PhD and already working for other prestigious firms, who take the time to solve the exercises and apply just to bring value to the company. Even worse, being caught in a manifest error, HR did not even bother to provide justifications and show the solution to a team of people with at least minimum background in mathematics (I wonder how she decided my solution to be wrong). That is the reason why such companies fail on the long run: they miss the good candidates (who end up working elsewhere easily) due to stupidity of HR.