Apex domains cannot have CNAME records.
Question and response
Question
dig ns2.servidoreswebs.com. NS
Answer
ns2.servidoreswebs.com. 5 NS ns1.servidoreswebs.com.
ns2.servidoreswebs.com. 5 NS ns2.servidoreswebs.com.
Authority
The response has no authority records.
Additional
ns1.servidoreswebs.com. 4 A 167.250.4.4
ns2.servidoreswebs.com. 4 A 184.172.175.9
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0