Lock screen changed to the old style -Ubuntu 16.04-

Hi! I use Ubuntu 16.04 (Unity) on my Dell Inspiron-20-Model-3043 (touch screen).

My problem is that the lock screen (ctrl + alt + L) changed to the old style like the one in Ubuntu 10.10, and I don't know why exactly, I don't remember have done anything in particular.
maybe it changed after the installation of Unity 8 mir but I didn't notice it until 3 days later so I'm not sure. Something curious is that the login screen works perfectly

These are the commands I tried until now:

sudo dpkg-reconfigure lightdm
sudo service lightdm restart
sudo lightdm

But nothing works, and actually I'm not sure if LightDM controls also the lock screen or only the login screen