Unable to create a PPPoE connection in Ubuntu 18.04 LTS

My ISP provides PPPoE connection with username, password and service name and binds my MAC Address. Since I have connected my router to the WAN, the MAC Address of the router has been bound in their server by them. Whereas the IP Address and Gateway are set to be automatically obtained, and DNS addresses are manually given. My Desktop has been connected to the router and the network is working fine.

However, for the purpose of troubleshooting the network when it goes down, I need to connect directly to the computer. Therefore, I need to know how to configure a wired PPPoE connection directly in my computer, which has only one NIC. The network settings GUI does not allow setting up one.

Please guide me how to -

i) configure a PPPoE connection
ii) specify the username, password and service name, and
iii) clone my router's MAC address to my desktop

to be able to connect to the internet. The GUI provided in Ubuntu 18.04 Bionic Beaver (which is what I am using) does not provide for creating a PPPoE connection. The GUI should also allow use of a cloned MAC address for the PPPoE connection.

After referring to various community posts, I tried the following command (though I am not quite conversant with Linux commands) :

nmcli connection add con-name "..." type pppoe username ... password ... service ... parent (iface name of the NIC) autoconnect no ifname "*" save yes

The pppoe connection gets created but vanishes from the "Settings -> Network" GUI under "Wired" category after some time and some times gets listed under "Bluetooth" category (under Network Settings) before vanishing.

Also, neither the command nor the GUI, allows me to specify a cloned MAC address to the connection created using the above command.

Please get this issue addressed at the earliest.