Similar thing happened to me.. went through a very lengthy interview process and successfully passed it where they called me the day after and said that they were going to give me an offer the next day! I was ecstatic.
They then called me the next day and said "oh, yeah -- we aren't going to give you an offer" and wouldnt give me a reason.
The next time, they attempted to recruit me for the same position and I went through several days of phone interviews passing each one. Then I said -- "so you know, I interviewed for this position before and was told I would get an offer, but then didnt" they went back and checked and then said "Yeah we wont be continuing the interview process"
Then it happened a third time! Finally I sent the recruiter an email that said "This is the third time you have attempted to recruit me for this position -- Either offer me the job, with a salaray of X or take me out of your system and stop calling me"
They haven't called me since -- and I still have no idea why I am blacklisted.