Apex domains cannot have CNAME records.
Question and response
Question
dig dns-servicio.com. NS
Answer
dns-servicio.com. 5 NS ns3.acens.net.
dns-servicio.com. 5 NS ns7.acens.net.
dns-servicio.com. 5 NS ns4.acens.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0