Apex domains cannot have CNAME records.
Question and response
Question
dig movistar.com.ar. NS
Answer
movistar.com.ar. 4 NS nsvel1a.tgt.net.ar.
movistar.com.ar. 4 NS nsvia1a.tgt.net.ar.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0