Complex sentence: It is difficult to document the number of Rohingya who remain in the Internally Displaced Persons camps as the so called "Illigal people" were not permitted to register for the national census and the government refuses to address this minority Rohingya ethnic group by name.
Split into simpler sentences: It is difficult to document the number of Rohingya who remain in the Internally Displaced Persons camps as they were not permitted to register for the national census. The government refuses to address this minority Rohingya ethnic group by name.