Apex domains cannot have CNAME records.
Question and response
Question
dig grepvolmuk.com. NS
Answer
grepvolmuk.com. 5 NS ns1.grepvolmuk.com.
grepvolmuk.com. 5 NS ns2.grepvolmuk.com.
Authority
The response has no authority records.
Additional
ns1.grepvolmuk.com. 5 A 74.48.6.242
ns2.grepvolmuk.com. 5 A 142.44.219.255
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0