Apex domains cannot have CNAME records.
Question and response
Question
dig b621.net. NS
Answer
b621.net. 5 NS rdns1.benjojo.co.uk.
b621.net. 5 NS rdns2.benjojo.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0