Cannot remount /system partition even when rooted (Sony xperia M2)

I have a Sony xperia M2 D2303 with kitkat 4.4.4 and compilation number 18.3.1.C.1.17.
I have successfully rooted it using KingRoot v4.9.5.
Also I have checked that system is rooted using tools such as root checker and it says rooted.

Now, I am trying to remount /system partition as RW but without succcess.

I have googled and tried several solutions posted here but nothing works for me.

1. Access to /sys/kernel/security/sony_ric and try to disable sony ric security using:
   
   problem here is that sony_ric folder is empty, I mean, there is no "enable" file and I cannot create it as partition is RO (read-only).
   


2. Using ES file explorer or other file explorers as root I have tried to remount partition as RW but it fails.
   
   
   

   Code:

   
   

   ---

   echo 0 > enable

   ---

   
   


3. Using ROM Toolbox pro, and then from terminal emulator I have tried some commands:
   
   
   

   Code:

   
   

   ---

   su
mount -o remount,rw /system

   ---

   
   
   fails.
   
   
   
   

   Code:

   
   

   ---

   su
system/bin/mount -o remount,rw /system

   ---

   
   
   also fails.
   
   
   
   

   Code:

   
   

   ---

   adb shell
su
mount -o rw,remount /system

   ---

   
   
   also fails...
   


4. I have tried to install busybox but it fails as well.
   

So at this point I have no idea what to do... Any help will be highly appreciated.