Apex domains cannot have CNAME records.
Question and response
Question
dig si.ecritel.net. NS
Answer
si.ecritel.net. 5 NS ns-b.ecritel.com.
si.ecritel.net. 5 NS ns-a.ecritel.com.
si.ecritel.net. 5 NS ns-a.ecritel.fr.
si.ecritel.net. 5 NS ns-b.ecritel.fr.
Authority
The response has no authority records.
Additional
ns-a.ecritel.fr. 5 A 5.144.137.235
ns-a.ecritel.com. 5 A 213.182.56.91
ns-b.ecritel.fr. 5 A 195.200.113.7
ns-b.ecritel.com. 5 A 195.200.116.132
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0