Apex domains cannot have CNAME records.
Question and response
Question
dig rebel.com. NS
Answer
rebel.com. 5 NS ns-1559.awsdns-02.co.uk.
rebel.com. 5 NS ns-143.awsdns-17.com.
rebel.com. 5 NS ns-837.awsdns-40.net.
rebel.com. 5 NS ns-1509.awsdns-60.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0