Apex domains cannot have CNAME records.
Question and response
Question
dig lewtelnet-access.de. NS
Answer
lewtelnet-access.de. 5 NS ns1.lewtelnet.de.
lewtelnet-access.de. 5 NS ns2.lewtelnet.de.
Authority
The response has no authority records.
Additional
ns1.lewtelnet.de. 5 A 212.118.192.5
ns2.lewtelnet.de. 5 A 212.118.216.2
ns1.lewtelnet.de. 5 AAAA 2a02:f90:0:192:0:0:0:5
ns2.lewtelnet.de. 5 AAAA 2a02:f90:0:216:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0