Apex domains cannot have CNAME records.
Question and response
Question
dig telecom.pt. NS
Answer
telecom.pt. 5 NS ns4.telepac.pt.
telecom.pt. 5 NS ns.webside.pt.
telecom.pt. 5 NS vivaldi.telepac.pt.
telecom.pt. 5 NS ns2.webside.pt.
telecom.pt. 5 NS ns3.telepac.pt.
Authority
The response has no authority records.
Additional
ns.webside.pt. 5 A 62.48.131.10
ns2.webside.pt. 5 A 62.48.131.11
ns4.telepac.pt. 5 A 194.65.3.103
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0