Rejected after three rounds and the position is still open?

I’m quite devastated. I applied to a job that I was well qualified for in a specific industry (t-shirt print and sales). I went through three rounds of interview and the interviewers told me that they liked me and thought that I was a great fit. A few days after the third interview, I got an email saying that I was not picked for the job even though the job has not been filled yet. I believed that I was super qualified for the job and had years of experience in the industry. We haven’t even talked salaries yet so obviously money was not the issue. I do not know how to proceed. Should I email them? What should I even say?

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