Apex domains cannot have CNAME records.
Question and response
Question
dig 128-27.50.210.62.in-addr.arpa. NS
Answer
128-27.50.210.62.in-addr.arpa. 5 NS ns1.oxi-dedi.net.
128-27.50.210.62.in-addr.arpa. 5 NS ns2.oxi-dedi.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0