Apex domains cannot have CNAME records.
Question and response
Question
dig st1internet.com.br. NS
Answer
st1internet.com.br. 3 NS dns1.st1internet.com.br.
st1internet.com.br. 3 NS dns2.st1internet.com.br.
Authority
The response has no authority records.
Additional
dns1.st1internet.com.br. 3 A 45.180.218.251
dns2.st1internet.com.br. 3 A 45.180.216.251
dns1.st1internet.com.br. 3 AAAA 2804:60d4:0:3:0:0:0:3
dns2.st1internet.com.br. 3 AAAA 2804:60d4:0:4:0:0:0:3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0