Bot

Hi
In log of my website, there are many post/get from different bots.
When I try to disallow all with a robots.txt, the robots file immediately will be deleted!!
Why?

Also for example there are 3 lines of log:

GET /lrom6/Tarak—mehata–ka–ulta–chasma—ki—-actress—-babita-image-download.html HTTP/1.0
or
GET /mailto/index.php/vdzmzm/ctbwyszm.jsp
POST /wp-cron.php?doing_wp_cron=1470791516.7687809467315673828125

and its http response code is 200!!

This path ins’t appear in my hots at all.
plz help me