Apex domains cannot have CNAME records.
Question and response
Question
dig deltafibra.com.br. NS
Answer
deltafibra.com.br. 5 NS ns1.deltafibra.com.br.
deltafibra.com.br. 5 NS ns2.deltafibra.com.br.
Authority
The response has no authority records.
Additional
ns1.deltafibra.com.br. 5 A 168.195.132.249
ns2.deltafibra.com.br. 5 A 168.195.132.250
ns1.deltafibra.com.br. 5 AAAA 2804:340c:c001:4:168:195:132:249
ns2.deltafibra.com.br. 5 AAAA 2804:340c:c001:4:168:195:132:250
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0