Apex domains cannot have CNAME records.
Question and response
Question
dig ns2.cometatelecom.com.br. NS
Answer
ns2.cometatelecom.com.br. 5 NS ns1.cometatelecom.com.br.
ns2.cometatelecom.com.br. 5 NS ns2.cometatelecom.com.br.
Authority
The response has no authority records.
Additional
ns1.cometatelecom.com.br. 5 A 170.231.192.10
ns2.cometatelecom.com.br. 5 A 170.231.192.11
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0