Apex domains cannot have CNAME records.
Question and response
Question
dig 19.233.89.in-addr.arpa. NS
Answer
19.233.89.in-addr.arpa. 5 NS dns101.telia.com.
19.233.89.in-addr.arpa. 5 NS dns102.telia.com.
19.233.89.in-addr.arpa. 5 NS dns2.telia.com.
19.233.89.in-addr.arpa. 5 NS dns49.de.telia.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0