Apex domains cannot have CNAME records.
Question and response
Question
dig enno-kundenservice.de. NS
Answer
enno-kundenservice.de. 5 NS 213.239.242.238.
enno-kundenservice.de. 5 NS 213.133.100.103.
enno-kundenservice.de. 5 NS 193.47.99.3.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0