Apex domains cannot have CNAME records.
Question and response
Question
dig static.isp.telekom.rs. NS
Answer
static.isp.telekom.rs. 5 NS adonis.telekom.rs.
static.isp.telekom.rs. 5 NS odisej.telekom.rs.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0