As my IP provider restricts the number of network cards that can access the net so on ubuntu i needed to change the MAC address of my network card. It’s pretty easy, just two lines of command on terminal.
ifconfig eth0 down hw ether 01:02:03:04:05:06
ifconfig eth0 up
1st command down the network and change the MAC to 01:02:03:04:05:06 and 2nd command again up the network