Apex domains cannot have CNAME records.
Question and response
Question
dig netcorecloud.net. NS
Answer
netcorecloud.net. 4 NS ns31.constellix.com.
netcorecloud.net. 4 NS ns21.constellix.com.
netcorecloud.net. 4 NS ns51.constellix.net.
netcorecloud.net. 4 NS ns61.constellix.net.
netcorecloud.net. 4 NS ns11.constellix.com.
netcorecloud.net. 4 NS ns41.constellix.net.
Authority
The response has no authority records.
Additional
ns11.constellix.com. 4 A 96.45.80.1
ns21.constellix.com. 4 A 46.31.236.1
ns31.constellix.com. 4 A 43.247.170.1
ns41.constellix.net. 4 A 96.45.81.1
ns51.constellix.net. 4 A 46.31.237.1
ns61.constellix.net. 4 A 43.247.171.1
ns11.constellix.com. 4 AAAA 2600:180a:1001:0:0:0:0:1
ns21.constellix.com. 4 AAAA 2600:180b:2001:0:0:0:0:1
ns31.constellix.com. 4 AAAA 2600:180c:3001:0:0:0:0:1
ns41.constellix.net. 4 AAAA 2600:180a:4001:0:0:0:0:1
ns51.constellix.net. 4 AAAA 2600:180b:5001:0:0:0:0:1
ns61.constellix.net. 4 AAAA 2600:180c:6001:0:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0