Apex domains cannot have CNAME records.
Question and response
Question
dig nl1-tr100.supercp.com. NS
Answer
nl1-tr100.supercp.com. 5 NS ns5.supercp.com.
nl1-tr100.supercp.com. 5 NS ns6.supercp.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0