Apex domains cannot have CNAME records.
Question and response
Question
dig simtelecom.com.br. NS
Answer
simtelecom.com.br. 5 NS dns1.commcorp.net.br.
simtelecom.com.br. 5 NS dns2.commcorp.net.br.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0