Unprofessional Behavior During the Interview Process

I was interviewed in April 2020 and completed all three rounds on the same day. The first and second rounds were technical, and the third was a managerial discussion with the director (Hiring Manager). All rounds were conducted via Zoom.

One week later, I received a call from HR informing me that I had been selected. We discussed compensation, and they offered a very decent hike. The HR representative stated they would send the offer letter in a couple of days.

After another week passed without an offer, I followed up. HR then informed me they were no longer considering my candidacy, as the position was on hold.

This is completely unprofessional behavior by the team handling the interviews. I am unsure why they proceeded with the HR interview if they were not interested in selecting a candidate.

First round on DS. Second round on design. Third round on behavioural.