Apex domains cannot have CNAME records.
Question and response
Question
dig g9telecom.pt. NS
Answer
g9telecom.pt. 5 NS dns2.interacesso.pt.
g9telecom.pt. 5 NS dns2.nortenet.pt.
g9telecom.pt. 5 NS dns.nortenet.pt.
Authority
The response has no authority records.
Additional
dns.nortenet.pt. 5 A 212.13.34.246
dns2.nortenet.pt. 5 A 212.13.35.173
dns2.interacesso.pt. 5 A 212.13.35.117
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0