Oracle Software Engineer interview questions

Hiring process took 3 days and 6 rounds of interview. ~1 hour each. HR asked me to finish all 6 rounds in 2 days and scheduled virtual interview. The entire interview went well and the interviewers are very cool and focused. But, I was rejected at the end. I have spent almost 6-7 hours for giving the interview, and then I was told that I was rejected. The HR, who responded well till then started rejecting the call and when I asked for feedback over email, she didn't even care to respond back(even after multiple follow-ups). I don't really understand why these people don't care about the candidates once they are rejected. Common, I have wasted my 6-7 hours of time for the interview and you don't even give feedback about what went wrong? If you are so busy, don't schedule interviews then. I have all the right to understand what went wrong and correct myself. This is not expected from a reputed company. HR informed me that there is a BT(Behavioral test) round and it is non technical. But when I joined the interview, they started putting tech questions. When HR herself isn't clear of what round it is going to be, then God must help the candidates.

Three rounds in total. One 20 mins hr phone screen, one round 1-hour tech interview, and then 3-hour of tech interviews. After solving all tech problems and have nice conversations with interviewers, still get rejected in the end. No idea how to get passed.