Apex domains cannot have CNAME records.
Question and response
Question
dig iptelecom.pt. NS
Answer
iptelecom.pt. 5 NS ns.refertelecom.pt.
iptelecom.pt. 5 NS dns.refertelecom.pt.
iptelecom.pt. 5 NS ns03.refertelecom.pt.
Authority
The response has no authority records.
Additional
ns.refertelecom.pt. 5 A 81.90.62.137
dns.refertelecom.pt. 5 A 81.90.54.99
ns03.refertelecom.pt. 5 A 81.90.54.100
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0