Apex domains cannot have CNAME records.
Question and response
Question
dig mxt.net.br. NS
Answer
mxt.net.br. 5 NS ns1.mxt.net.br.
mxt.net.br. 5 NS ns2.mxt.net.br.
Authority
The response has no authority records.
Additional
ns1.mxt.net.br. 5 A 179.108.128.22
ns2.mxt.net.br. 5 A 179.108.128.21
ns1.mxt.net.br. 5 AAAA 2804:ec4:9001:0:0:0:0:301
ns2.mxt.net.br. 5 AAAA 2804:ec4:9001:0:0:0:0:305
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0