Apex domains cannot have CNAME records.
Question and response
Question
dig heimfuelservice.com. NS
Answer
heimfuelservice.com. 5 NS ns-328.awsdns-41.com.
heimfuelservice.com. 5 NS ns-1842.awsdns-38.co.uk.
heimfuelservice.com. 5 NS ns-218.awsdns-27.com.
heimfuelservice.com. 5 NS ns-1534.awsdns-63.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0