I've an active subscription with VPNUnlimited, and they have sent a few settings in order to be able to use OpenVPN client with their service. (they have sent me pre-made .ovpn files for each of their servers)
the thing is, I've followed a tutorial to setup OpenVPN in my raspberry pi, and whenever I start the OpenVPN client with the .ovpn file, it authenticate and connects successfully.
this looks great but the problem is after a successfull connection, it looks like DNS configuration is not correct as any trial to navigate/ping any domain name fails, although pinging any IP is succeeded, so it's normally state that there is a DNS problem.
disconnecting the session will restore back the ability to resolve domain names normally and use the built-in web browser to browse websites.
I've searched for a while and found that one possible fix is to add the following line (provided from this question) to the client.conf file in order to force the client to use Google DNS:
dhcp-option DNS 8.8.8.8
but unfortunately it's not working.
this is what is on my screen as a result on connecting to openvpn:

and this is the ifconfig after the connection is established:

and this is the ifconfig result when I disconnect the OpenVPN client:

I hope I could clarify the situation, and if anyone can help me to setup the proper configuration to make my raspberry pi use google DNS (or anything that would work) I would much appreciate it as I can't figure it out yet.