I was told i was the preferred candidate and then nothing

The title says it all. The recruiter told me i was the one they preferred. The ED told me while i was leaving the room not to worry and that it would all go just fine. And then silence. I sent an email to follow up and they told me they needed me to give them my NIN. And then again silence. I called 2-3 times but no answer. I checked with my previous employers and they confirmed that none has contacted them for references. So, what happened :/ How come i was the one they preferred and then nothing? What can explain this weird silence? And why would they let me know i was the preferred one if they were not going to hire me?