DDA Cheating

My father Mr Jagdish chander Kukreja filled an application for the DDA lig flat 1979 and the draw was held in 1999 and he was one of the  successful applicants.he filled the application on "hire purchase" and it came on "cash down" and when he asked to change the same. Authorities denied to change the same and no reason was given. And due to lack of funds ,lack of knowledge and lack of guidance from authorities ,as he could not pay the entire amount in one go as per his income. It was told to him to cancel the flat or else he will loose the booking amount of 5k as well .they visited several times to dda offce but nothing was done at that time. So he was left with no other option but to cancel the flat ....I request to please advise the way fwd