Zinier Product Manager interview questions

I have gone through 5 rounds of interviews over 2 weeks. Each round was scheduled only after the positive feedback from the previous round. After the last round, HR informed me over the PHONE CALL that I have been selected and asked me to share all my relevant documents. She then scheduled my compensation discussion with another HR  and confirmed the final offer again over PHONE CALL. Anyways.. after 4 days of PHONE CALL confirmation and not yet receiving the offer letter I checked with HR and was informed that it's still under the approval process and I should receive within a day or two. And now comes the weird part, after another 3 days the HR comes back only to inform that one of the interview panelists from the engineering domain is not sure of his/her feedback and would like me to work on a take-home case study as one more round... After arguing about how can this be true HR tells me that this happens all the time and since they did not send anything over the email so nothing was final from their side... How can a company discuss and finalize compensation and then after a week tell you that you have to work on a big assignment!! Also, in my 5th and last round of interviews, I was told by the panel that is my final round and there will be no further elimination rounds... NO-VALUE OF THEIR OWN WORDS!! Clearly, the recruitment team needs to get their act together and so that this does not happen again with any other candidate.. Also, how come someone who has passed positive feedback can rethink after an offer has been made to the candidate ..this is so unethical. I am glad that God saved me from this company and that person who changed his feedback to work with.