Try out the following commands:
sudo service networking restart
sudo /etc/init.d/networking restart
or
nmcli device set [device] managed true
Check Networking Status
/etc/init.d/networking status
Stop Networking
sudo /etc/init.d/networking stop
Start Networking
sudo /etc/init.d/networking start
Restart Networking
/etc/init.d/networking restart
To start Network Manager :
service NetworkManager start
or
systemctl start NetworkManager
To stop Network Manager:
service NetworkManager stop
or
systemctl stop NetworkManager
To restart Network Manager:
service NetworkManager restart
or
systemctl restart NetworkManager