Apex domains cannot have CNAME records.
Question and response
Question
dig customer.ggaweb.ch. NS
Answer
customer.ggaweb.ch. 2 NS ns1.ggamaur.net.
customer.ggaweb.ch. 2 NS ns3.ggamaur.net.
customer.ggaweb.ch. 2 NS ns2.ggamaur.net.
Authority
The response has no authority records.
Additional
ns1.ggamaur.net. 2 A 213.160.40.2
ns2.ggamaur.net. 2 A 213.160.40.34
ns3.ggamaur.net. 2 A 213.160.41.2
ns1.ggamaur.net. 2 AAAA 2a02:5c0:1:9:0:0:0:2
ns2.ggamaur.net. 2 AAAA 2a02:5c0:1:9:0:0:0:34
ns3.ggamaur.net. 2 AAAA 2a02:5c0:1:11:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0