Apex domains cannot have CNAME records.
Question and response
Question
dig mtfibra.mx. NS
Answer
mtfibra.mx. 5 NS ns2.mtfibra.mx.
Authority
The response has no authority records.
Additional
ns2.mtfibra.mx. 5 A 38.45.247.12
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0