Apex domains cannot have CNAME records.
Question and response
Question
dig teresto.net. NS
Answer
teresto.net. 5 NS ns2.teresto.net.
teresto.net. 5 NS ns3.teresto.net.
teresto.net. 5 NS ns4.teresto.net.
teresto.net. 5 NS ns1.teresto.net.
Authority
The response has no authority records.
Additional
ns1.teresto.net. 5 A 212.88.128.10
ns2.teresto.net. 5 A 217.31.66.232
ns3.teresto.net. 5 A 217.31.71.30
ns4.teresto.net. 5 A 212.88.128.70
ns1.teresto.net. 5 AAAA 2a02:5a0:1fff:ffff:0:0:0:10
ns2.teresto.net. 5 AAAA 2a02:3a8:100:0:0:0:0:100
ns3.teresto.net. 5 AAAA 2a02:3a8:200:0:0:0:0:200
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0