Apex domains cannot have CNAME records.
Question and response
Question
dig mdzinternet.com.ar. NS
Answer
mdzinternet.com.ar. 5 NS ns2.hrdns.info.
mdzinternet.com.ar. 5 NS ns1.hrdns.info.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0