Apex domains cannot have CNAME records.
Question and response
Question
dig cm-alcoutim.pt. NS
Answer
cm-alcoutim.pt. 5 NS ns2.vf-portal.com.
cm-alcoutim.pt. 5 NS ns2.vf-host.com.
cm-alcoutim.pt. 5 NS ns1.vf-host.com.
cm-alcoutim.pt. 5 NS ns1.vf-portal.com.
Authority
The response has no authority records.
Additional
ns1.vf-host.com. 5 A 91.199.116.236
ns1.vf-portal.com. 5 A 91.199.116.236
ns2.vf-host.com. 5 A 68.219.230.185
ns2.vf-portal.com. 5 A 68.219.230.185
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0