Apex domains cannot have CNAME records.
Question and response
Question
dig unetelecom.psi.br. NS
Answer
unetelecom.psi.br. 5 NS pns11.cloudns.net.
unetelecom.psi.br. 5 NS pns13.cloudns.net.
unetelecom.psi.br. 5 NS pns12.cloudns.net.
unetelecom.psi.br. 5 NS pns14.cloudns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0