Apex domains cannot have CNAME records.
Question and response
Question
dig tigo.com.bo. NS
Answer
tigo.com.bo. 5 NS dns1.wimaxtigo.bo.
tigo.com.bo. 5 NS dns2.wimaxtigo.bo.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0