Center on Addiction interview questions

I applied to a part-time, impermanent role online and was called in for an interview. After the interview, I was given four days to complete an assignment and get three references to HR. HR contacted my three references immediately, asking for answers to ten open-ended questions. After this process, I emailed HR three times until I finally got a rejection letter about 1.5 months later. I was shocked by this process and asked for any and all feedback about my application/interview because I was very interested in the role and would like to improve on any potential weaknesses in regard to communications for healthcare non-profits. Not surprisingly, I never heard a response. I'm shocked that this organization would treat a part-time, impermanent role like this. As a freelancer, my references are extremely valuable as I utilize them more than a full-time employee would. I'm very disappointed by the whole experience and would like an explanation.