Apex domains cannot have CNAME records.
Question and response
Question
dig 3.14.62.static.jazztel.es. NS
Answer
3.14.62.static.jazztel.es. 5 NS dns2.jazzvisp.com.
3.14.62.static.jazztel.es. 5 NS dns1.jazzvisp.com.
Authority
The response has no authority records.
Additional
dns1.jazzvisp.com. 5 A 62.14.4.66
dns2.jazzvisp.com. 5 A 87.216.7.3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0