Apex domains cannot have CNAME records.
Question and response
Question
dig combellgroup.com. NS
Answer
combellgroup.com. 5 NS ns1.combell.eu.
combellgroup.com. 5 NS ns3.combell.net.
combellgroup.com. 5 NS ns4.combell.net.
Authority
The response has no authority records.
Additional
ns1.combell.eu. 4 A 89.44.166.48
ns3.combell.net. 4 A 83.217.73.172
ns4.combell.net. 4 A 86.39.202.67
ns1.combell.eu. 4 AAAA 2a00:1c98:50:0:0:0:0:50
ns3.combell.net. 4 AAAA 2a00:1c98:0:0:0:0:53:1
ns4.combell.net. 4 AAAA 2001:1598:0:101:0:0:0:3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0