Can't mount /system as RW on Xperia T3

[Szmok]

So I recently rooted my Xperia T3 using KingRoot... It was successful, various root checkers didn't report any problems but I just can't delete any system apps, move, cut, anything. Was trying to do this with ES Root Explorer (it has option to make /system RW but it doesn't work), Root Explorer, even system apps removers. Titanium Backup also didn't make it.
I tried using Total Commander and its remount function too. At last I tried to do this through terminal with "
mount -o rw,remount -t ext4 /dev/block/platform/..." command and it just says "operation not permitted"

As you can see I ran out of options (at least out of these I know). I'm still a noob so it's really possible that I'm doing something wrong.

I'm using android 4.4.4, original from Sony.
Thank you for your time!

 

[scary alien]

Hello and welcome to our AndroidForums, @Szmok .

It sounds/looks like you've done your homework and more, trying all of the obvious and non-obvious ways to remount /system in read-write mode...

I'm guessing you've got a locked bootloader or a kernel that has extra measures in-place to keep you from getting that filesystem/partition out of read-only mode .

Not sure what else to suggest at this point...