Spoke to HR and then they give an assignment. They have not changed there assignment from past 6 years, I applied in college for internship to applying for experience role its same. They didn't respond for more than a month for the assignment

The interview process started with the HR approaching with a few questions. They asked me to do an assignment, which they specifically asked me not to put in my portfolio as it was their project done for a client (kinda weird but I was like okay). I did the assignment in under 4 days with everything and more than what was expected. They had given 6-7 days to do the same. After submitting the assignment they asked me to wait for a week. After following up they asked me to wait for another week. And this kept happening for 1 month. The HR said and I quote "the assignment has mixed feedback and I have no clear feedback, kindly wait for a week". After waiting for weeks, they said that the set of skills I have didn't match their requirements. I followed up again a couple of times to get a clear feedback as to what skills they were looking for. I am still in a dilemma whether they used my assignment for their client and own purposes to gather ideas.