Apex domains cannot have CNAME records.
Question and response
Question
dig iom.com. NS
Answer
iom.com. 5 NS pebbles.iom.com.
iom.com. 5 NS hoppy.iom.com.
iom.com. 5 NS barney.advsys.co.uk.
Authority
The response has no authority records.
Additional
hoppy.iom.com. 5 A 217.23.163.140
barney.advsys.co.uk. 5 A 217.23.160.50
pebbles.iom.com. 5 A 83.218.14.53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0