Apex domains cannot have CNAME records.
Question and response
Question
dig 250.10.38.in-addr.arpa. NS
Answer
250.10.38.in-addr.arpa. 4 NS ns1.tecnovenca.net.
Authority
The response has no authority records.
Additional
ns1.tecnovenca.net. 4 A 45.179.164.10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0