Problem with our nameserver

Hello, I am a beginner in this sort of stuff so please bear that in mind when answering.

I recently bought a dedicated server from leaseweb, unfortunately they've asked for more money to even the most simple of tasks and I have yet to make my new server function.

What I want is to have 2 nameservers, ns1.mydomain.gr and ns2.mydomain.gr.

I have gone to my domain registrar and pointed the domain name to the ip addresses-nameservers which were given to me through their support.

I went to WHM, used ns1.mydomain.gr and 2 in the basic setup.

I couldn't use them in "Nameserver IPs" because the "Assigning Ip Address for ns1.inath.net" was indefinite, never finished.

Any ideas on what to do ?

PS. If this has been answered before, you can always point me to the right direction.