Apex domains cannot have CNAME records.
Question and response
Question
dig corporativafiber.com.br. NS
Answer
corporativafiber.com.br. 5 NS ns1.corporativafiber.com.br.
corporativafiber.com.br. 5 NS ns2.corporativafiber.com.br.
Authority
The response has no authority records.
Additional
ns1.corporativafiber.com.br. 5 A 131.161.104.104
ns2.corporativafiber.com.br. 5 A 131.161.105.105
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0