WHM: How to associate a new domain name with an existing account

So, long saga, but we have a domain name domaink.net which is set up on our server.

The domain needs to point to an existing account on our server. The DNS is created from scratch in the WHM and is associated with the correct account, however, when the domain name is entered on the browser it always only reaches the alphabetically first domain on the server.

Current DNS:

domaink.net.    86400    IN    SOA    ...
domaink.net.    86400    IN    NS    ns1.server.co.uk.
domaink.net.    86400    IN    NS    ns2.server.co.uk.
domaink.net.    14400    IN    A    123.456.78.90
mail    14400    IN    CNAME    domaink.net.
www    14400    IN    CNAME    domaink.net.
ftp    14400    IN    CNAME    domaink.net.
ns2    3600    IN    A    123.456.78.90
ns1    3600    IN    A    123.456.78.90
localhost    3600    IN    A    127.0.0.1

We have also tried to add "Alias" and similar "Domain" to the CPanel Domain area but this refuses to work because the domain DNS already exists, but even if we delete the DNS in WHM and retry, it refuses to add saying that the IP doesn't point to this server, even though the IP does point to this server! 

The IP address of the SOA server (appears different from our own server which runs DNS for some reason) is 213.171.192.249 and adding this to the "remote name server" under WHM --> Configure Remote Service IPs as per the feedback notice but the error message from the CPanel --> DNS --> Alias screen still says that this needs to be done. The DNS server has been restarted several times to no effect.

How do we set (manually editing files on the server or otherwise via WHM) that the domain domaink.net reaches the correct CPanel account?

Thanks