Apex domains cannot have CNAME records.
Question and response
Question
dig iplanisp.com.ar. NS
Answer
iplanisp.com.ar. 3 NS dns1.iplanisp.com.ar.
iplanisp.com.ar. 3 NS dns2.iplanisp.com.ar.
iplanisp.com.ar. 3 NS dns3.iplanisp.com.ar.
Authority
The response has no authority records.
Additional
dns1.iplanisp.com.ar. 3 A 162.159.26.103
dns2.iplanisp.com.ar. 3 A 190.2.2.250
dns3.iplanisp.com.ar. 3 A 162.159.27.69
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0