Apex domains cannot have CNAME records.
Question and response
Question
dig telefonicaonline.com. NS
Answer
telefonicaonline.com. 5 NS dns2.movistar.es.
telefonicaonline.com. 5 NS dns1.movistar.es.
Authority
The response has no authority records.
Additional
dns1.movistar.es. 5 A 81.47.201.19
dns2.movistar.es. 5 A 81.47.201.27
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0