Apex domains cannot have CNAME records.
Question and response
Question
dig cronostelecom.com.br. NS
Answer
cronostelecom.com.br. 5 NS cpsp01.volare.host.
cronostelecom.com.br. 5 NS cpsp02.volare.host.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0