Apex domains cannot have CNAME records.
Question and response
Question
dig cable.net.co. NS
Answer
cable.net.co. 3 NS ns2.telmexla.net.co.
cable.net.co. 3 NS ns11.telmexla.net.co.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0