Mayfair Granite interview questions

It is my belief that they are interviewing people to gather their ideas for further use without having to hire/pay anyone. They have been interviewing for the same role for months and have been hosting multiple interviews without providing any feedback. For my interview I was asked to produce a 30 day plan for how I would use social media to market their business. Other people have been told to do the same. They have had plenty of strong candidates with degrees in marketing, who currently are employed within social media marketing, yet they interview for this role non-stop over the course of at least MONTHS - with each interview gathering more ideas from young marketing experts. No feedback received, even months later, no rejection email or anything, just reposting job adverts every week for the same role and interviewing constantly. My interview was HOURS long, I believe it was 2-3 hours just sat with their HR/Marketing Manager. Yes, this one person has both roles. They have no HR department and it is not a professional set up. The questions asked by this individual were very inappropriate/discriminatory for HR to ask (such as whether I had a partner/kids/if I saw myself having kids) and I could easily take this further. They appear wary of young women joining and then having to pay maternity leave (they admitted their workplace is very male dominated). Overall a very bizarre interview, and post-interview I received no further communication. Ideas from interviews have been used with no compensation, and it appears they are constantly gathering more ideas through the use of interviews without any intention to hire.