Apex domains cannot have CNAME records.
Question and response
Question
dig altice.pt. NS
Answer
altice.pt. 5 NS ns10.ptempresas.pt.
altice.pt. 5 NS ns2.ptempresas.pt.
altice.pt. 5 NS ns1.ptempresas.pt.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0