Apex domains cannot have CNAME records.
Question and response
Question
dig impsat.com.ar. NS
Answer
impsat.com.ar. 4 NS ns1.gblx.net.ar.
impsat.com.ar. 4 NS ns2.gblx.net.ar.
Authority
The response has no authority records.
Additional
ns1.gblx.net.ar. 4 A 8.243.1.18
ns2.gblx.net.ar. 4 A 8.243.1.34
ns1.gblx.net.ar. 4 AAAA 2001:13b4:0:101:0:0:0:2
ns2.gblx.net.ar. 4 AAAA 2001:13b4:0:102:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0