Apex domains cannot have CNAME records.
Question and response
Question
dig rogsurvey.de. NS
Answer
rogsurvey.de. 5 NS ns-1223.awsdns-24.org.
rogsurvey.de. 5 NS ns-1745.awsdns-26.co.uk.
rogsurvey.de. 5 NS ns-155.awsdns-19.com.
rogsurvey.de. 5 NS ns-954.awsdns-55.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0