Apex domains cannot have CNAME records.
Question and response
Question
dig serviciodns.es. NS
Answer
serviciodns.es. 5 NS ns-208-c.gandi.net.
serviciodns.es. 5 NS ns-236-a.gandi.net.
serviciodns.es. 5 NS ns-212-b.gandi.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0