Grab Software Engineer - Front End interview questions

Got automated emails from GABI bot to schedule the first round(DS, ALGO) for an hour. Why would you ask such difficult questions for the frontend role? Why is a backend engg taking interview for frontend role? I solved ~ both problems in interview. No feedback or update even after 4 days. Sent email, no update. Called HR, "we have already filled this position now". No courtesy to inform. No apology. From whole terrible experience, it looks like they were just in a mood to waste my time.