Hi raj,
There are so many ways of coding to call reports from forms

I normally use

Please use Run_report_object example in Oracle

That will help you with example
DECLARE
repid REPORT_OBJECT;
v_rep VARCHAR2(100);
rep_status varchar2(20);
BEGIN
repid := find_report_object('report4');
v_rep := RUN_REPORT_OBJECT(repid);
END;