Quandoo Middle Software Engineer - Java/Kotlin interview questions

Interview process sounded good and effective but it wasn't. I had a first interview with HR, a very kind woman and she explained me about the company and about the interview process. Next day they sent me a home task (a code to be improved), asking to send back in 7 days but if I could tell if I would need more time and it wouldn't be a problem (their words). I sent the finished task 6 days later (containing everything they asked for and more functionalities) and they took 15 days to reply back. Their reply said "This is due to the high number of suitable candidates that better fill the requirements of the position" but no feedback related to the task. I didn't waste time on the task because I considered it as a practice but this is very frustrating.