SQLPLUS hangs when I connect with Service name

I am able to connect to the database without the service name, but when I provide the service name, it just hangs.

For ex:  sqlplus user/password    ( works well)

It connects to the required database. but when I give service name on this host, it simply hangs

Ex; sqlplus user/password@service_name { hangs}

I am able to connect to the other remote database using service name.... I feel there is no issue with the tnsnames.ora syntax.

I confirm ORACLE_SID, ORACLE_HOME and TNS_ADMIN parameters are exported and they are properly set.

FYI.. local naming service testing also hangs using netca config assistant too.