Processing time for visitors visa

[suK287]

Hi, 

My parents applied for visitors visa in the year of 2015. My mother being a state govt employee got visa for 10 years where as my father who is a central govt employee was given a white slip and his case was kept in administrative processing requesting for additional documents.However after 2 months of wait, he got visa for 1 year. By then he had to drop his plan of visit. Later this year he had to repeat the whole process and ended up getting a white slip again. But its almost 4 months now and status still shows administrative processing. Can you please help me with this. I don't understand what to do next.