Apex domains cannot have CNAME records.
Question and response
Question
dig semfronteiras.net.br. NS
Answer
semfronteiras.net.br. 5 NS ns1.rr64.com.br.
semfronteiras.net.br. 5 NS ns2.rr64.com.br.
Authority
The response has no authority records.
Additional
ns1.rr64.com.br. 5 A 134.209.118.110
ns2.rr64.com.br. 5 A 200.219.149.195
ns1.rr64.com.br. 5 AAAA 2604:a880:400:d1:0:0:c4b:a001
ns2.rr64.com.br. 5 AAAA 2801:80:1920:2:200:219:149:195
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0