Lastline interview questions

The selection process involves 4 stages: the first is a screening interview with HR, then there are two more technical interviews: the first is just at a high-level, the second one goes a bit deeper into the technical expertise required for the position. The last stage is a coding challenge at the end of which there is another interview in which you go through your code and explain your choices. All the interviews were very kind and easy-going, and they do help you if you are in trouble. It was definitely a nice experience. All interviews can be done remotely.

After a one hour phone interview with the recruter I've been invited to take a tech challenge. The challenge was a CTF style test. I've spent time and I made an effort to complete all the test, I've found 6 out of 8 flags and I've completed all the requests. Three days after submitting the test, I've received a really basic and sterile email: "After closer examination of your application for the position of Technical Support Engineer, we've decided not to progress with your candidacy on this occasion. We encourage you to stay connected with us and should other positions become available that you feel would be a good match for your skillset please don't hesitate to apply." I've sent two email requesting feedbacks about my perforamnce and explanations about my failure, even to have the solutions of the challenge but NOTHING. I've found this really unprofessional, disrespectful and not serious at all.