And I submitted my KYC documents before to that exchange, I got mail that it got rejected but they did not say why?...what was lacking in my kyc documentation?.

I got my KYC approved in every other exhange - Bitrex, Binance and Wazirx and other exchanges as well.

Also they are confusing... hide your last 7 digits in your id??? ...so I take extra efforts in editing the proof for them...hell they are, and no one is there to explain this... I have to read and understand.

So much to read , not all the time you can understand the requirements when read, you get doubths, no support to answer your quiries.

It's automated, go look at the FAQ and if you submit documents as asked , it would et approved it seems... anyway!!