Fragomen Associate Consultant - Case Processing interview questions

There were 4 rounds of interview. I have cleared all the rounds. The last round was with HR where we discussed about the package, job designation, duties every thing and asked me to confirm the date. The next day I mailed them the confirmation date of joining. Received no response. Later on I came to know that my application was on hold. Felt horrible since the interview process took me one whole day and the interview ended up in a positive manner but i everything went in vain. They told me there was no opening and so my application was kept on hold, also they would contact later when more position opens. I don't understand their process? Literally, puzzled of their response.