Apex domains cannot have CNAME records.
Question and response
Question
dig onitel.com.br. NS
Answer
onitel.com.br. 5 NS ns2.onitel.com.br.
onitel.com.br. 5 NS ns1.onitel.com.br.
Authority
The response has no authority records.
Additional
ns1.onitel.com.br. 5 A 216.98.208.2
ns2.onitel.com.br. 5 A 216.98.208.9
ns1.onitel.com.br. 5 AAAA 2804:3c60:0:0:0:0:0:2
ns2.onitel.com.br. 5 AAAA 2804:3c60:0:0:0:0:0:9
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0