Slack interview questions

A recruiter at Slack reached out to me and I scheduled a call. We talked about my current role and past experience, plus what I was looking for in a new role. Normally, the next step would have been to start working on a take-home exercise, but I expressed that I wasn't doing that until I thought I might even be a fit for the company. I was given the opportunity to schedule a call with an engineering director, where we talked largely about the company culture and what Slack was working on (as well as answering some questions I had about company structure and makeup). I then moved forward with the take-home exercise. The recruiter told me that, as a general guideline, it should take 3 - 4 hours, though they give you a week to do it. I certainly couldn't have finished it in 3 - 4 hours and ended taking about 8 - 10 on it. I submitted what I had at that point instead of adding all the bells and whistles to the code (it worked and did what was asked). A few days later I got a rejection email without any feedback. I'm not really sure what they were expecting or why what I provided didn't meet the requirements (at least for a follow-up conversation). I have a lot of theories, but without feedback I really don't know what was wrong with what I provided. The challenge itself isn't a difficult one, though it's something you could spend 40 hours or more on getting perfect. It's difficult to tell when to stop working on it. I should note that I was told that the take-home exercise is the only coding done during the interview process (I assume that means there aren't any whiteboard coding sessions for the on-site).

Can someone tell them, this is not a fish market but a real professional company ? They have been keeping me hanging for a while like I read in another reviews, same happened to me. The HR talked to me, and gave me a programming assignment after everything looked good. They said to finish it in a week. I finished the same weekend ( in about 2 days ), and it's been 2 weeks, they keep postponing to get back to me. My website code checks who has logged in, and I don't see they even bothered to look at the website. FCK this company. Someone teach them some professionalism. Also, there are million other ways to market your company. I finally sent an email to HR to withdraw my application without them getting back to me. Yah felt good and relieved. Never working for this company again.