Apex domains cannot have CNAME records.
Question and response
Question
dig telmexla.net.co. NS
Answer
telmexla.net.co. 5 NS ns1.telmexla.net.co.
telmexla.net.co. 5 NS ns7.telmexla.net.co.
Authority
The response has no authority records.
Additional
ns1.telmexla.net.co. 5 A 190.157.8.71
ns7.telmexla.net.co. 5 A 190.157.8.71
ns1.telmexla.net.co. 5 AAAA 2800:480:ff78:c:0:0:0:1
ns7.telmexla.net.co. 5 AAAA 2800:480:ff78:c:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0