Delhi Development Authority (DDA) — illegal construction on terrace in DDA SFS flats

Address: North West Delhi, Delhi

We are living in a DDA SFS Flats in Pocket- I, Platinum Enclave ,Sector 18 ,Rohini , New Delhi. It is a four-storied flats where the terrace is common to all(as mentioned in the registry and all the papers). but after 9 years the top floor residents are building the rooms with kitchen and bathroom on the common terrace and no one is trying to stop the illegal work which is happening in front of all the people and the authorities. Why this all is happening? how the authority is allowing them to do this construction?
i would like to have a early response!!