Apex domains cannot have CNAME records.
Question and response
Question
dig 105.209.181.in-addr.arpa. NS
Answer
105.209.181.in-addr.arpa. 5 NS ns2.dcarsat.com.ar.
105.209.181.in-addr.arpa. 5 NS ns1.dcarsat.com.ar.
Authority
The response has no authority records.
Additional
ns1.dcarsat.com.ar. 5 A 186.33.224.10
ns2.dcarsat.com.ar. 5 A 186.33.225.10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0