Apex domains cannot have CNAME records.
Question and response
Question
dig aaa-internetshops.de. NS
Answer
aaa-internetshops.de. 5 NS ns2.teamnet.de.
aaa-internetshops.de. 5 NS ns1.teamnet.de.
aaa-internetshops.de. 5 NS ns3.teamnet.de.
Authority
The response has no authority records.
Additional
ns1.teamnet.de. 3 A 80.87.112.130
ns2.teamnet.de. 3 A 80.87.112.131
ns3.teamnet.de. 3 A 80.87.114.2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0