The assignment document which you are sent upfront provides very clearly that you will only get paid for the assignment if you deliver it and it meets all requirements and is passed by QA on the first attempt - please read it again. If you delivered an assignment with issues and it got turned down by QA then you are not to expect to get paid. If the QA allowed you to resubmit, then it is to allow you the attempt for you to try to fix the issues - however, as per your own story, other issues were still there on second submission. Furthermore we never allow candidates a third submission, so I don't know where "again and again" came from - if you sent us a third submission out of your own initiative and without our solicitation, then it was your own decision to do so. So please do not complain. We have had plenty people who sent us good test assignments and we paid them and offered them jobs as well - we make everything clear in our rules upfront, our expectations of quality, including the expectation that you need to figure out your own UX and make it up to our standards is explained in the assignment document (if you don't like it you don't have to do the assignment) and if you screw up the assignment, then you only have yourself to blame.

You were asked in writing before the interview to read the job description and understand the details of the job, which has been described in great length in publicly available job description. You showed up to a call and failed to produce an answer that demonstrated any awareness of the job details besides just knowing the job title. You were rejected as result for failing to follow a simple instruction. Don't complain, please.