Crontab @reboot not working

I need macchanger to automatically randomize my mac address after each reboot so I found this command line to put in crontab -e:
@reboot macchanger -r eth0

After puting it in crontab -e, i've rebooted the system and checked my mac address with ifconfig eth0 but it was still my original mac address.

I would like to know how can I make it work.

I have already tried those cammands:
@reboot ifconfig eth0 down && macchanger -r eth0 && ifconfig eth0 up

@reboot service NetworkManager stop && macchanger -r && NetworkManager start

but they both did not work as well.

Ps: when I do macchanger -r eth0 in terminal, it works just fine and change my mac address without any problems