Apex domains cannot have CNAME records.
Question and response
Question
dig customcall.us. NS
Answer
customcall.us. 5 NS pdns99.ultradns.com.
customcall.us. 5 NS pdns99.ultradns.biz.
customcall.us. 5 NS pdns99.ultradns.org.
customcall.us. 5 NS pdns99.ultradns.net.
Authority
The response has no authority records.
Additional
pdns99.ultradns.biz. 4 A 156.154.66.99
pdns99.ultradns.net. 4 A 156.154.65.99
pdns99.ultradns.org. 4 A 156.154.67.99
pdns99.ultradns.biz. 4 AAAA 2610:a1:1015:0:0:0:0:87
pdns99.ultradns.net. 4 AAAA 2610:a1:1014:0:0:0:0:87
pdns99.ultradns.org. 4 AAAA 2001:502:4612:0:0:0:0:87
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0