ns51.dnsever.com has no CNAME records.
Question and response
Question
dig ns51.dnsever.com. NS
Answer
The response has no answer records.
Authority
dnsever.com. 4875 SOA ns7.dnsever.com. admin.dnsever.com. 1747039760 86400 600 1209600 14400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0