Apex domains cannot have CNAME records.
Question and response
Question
dig onnettelecom.com.br. NS
Answer
onnettelecom.com.br. 4 NS ns1.onnettelecom.com.br.
onnettelecom.com.br. 4 NS ns2.onnettelecom.com.br.
Authority
The response has no authority records.
Additional
ns1.onnettelecom.com.br. 4 A 177.85.0.250
ns2.onnettelecom.com.br. 4 A 177.85.0.254
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0