FoodFund interview questions

I applied for this company through LinkedIn. They reached out to me to schedule an interview. I had a 45 minutes interview with their Chief Operating Officer. Then got an email regarding that I have made it to the second round. They asked me for a design challenge that was a problem of their site. I was inexperienced then and didn't know it is unethical to ask someone for ideating to solve a problem for free. I accepted it and sent them a comprehensive report on the problem, solutions, my approach, and the ideas that I came up with. They never got back to me and didn't reply to any of my emails inquiring about my application.