Apex domains cannot have CNAME records.
Question and response
Question
dig simplyspamfree.com. NS
Answer
simplyspamfree.com. 5 NS ns-100.awsdns-12.com.
simplyspamfree.com. 5 NS ns-1484.awsdns-57.org.
simplyspamfree.com. 5 NS ns-997.awsdns-60.net.
simplyspamfree.com. 5 NS ns-2028.awsdns-61.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0