Apex domains cannot have CNAME records.
Question and response
Question
dig addr.refertelecom.pt. NS
Answer
addr.refertelecom.pt. 4 NS ns.refertelecom.pt.
addr.refertelecom.pt. 4 NS ns.addr.refertelecom.pt.
Authority
The response has no authority records.
Additional
ns.refertelecom.pt. 4 A 81.90.62.137
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0