can't call function to delete the table

Hello Experts,
Would you please help me why I can't call the function to delete table and insert data from another table?  Simple deletion and insert from one to other are fine 
DELETE FROM bnft_hist_actn_ldim;
INSERT INTO bnft_hist_actn_ldim SELECT stg.bnft_hist_actn_id, stg.bnft_hist_actn_src_cd, stg.bnft_hist_actn_desc, stg.mig_filenameFROM stg_bnft_hist_actn_ldim stg;
-----but when I put in the stored function, it's not working.
My stored function script is:

CREATE OR REPLACE FUNCTION pr_mig_stg_bnft_hist_actn_ldim(OUT v_Ret integer)AS $$
DECLARE         v_ErrorCode             varchar(32);        v_ErrorMsg              varchar(512);        v_Module                varchar(32) = 'pr_mig_stg_bnft_hist_actn_ldim';        BEGIN
    DELETE FROM bnft_hist_actn_ldim;
    INSERT INTO bnft_hist_actn_ldim     SELECT stg.bnft_hist_actn_id, stg.bnft_hist_actn_src_cd, stg.bnft_hist_actn_desc,          stg.mig_filename    FROM stg_bnft_hist_actn_ldim stg;
RETURN NEW;
    v_Ret := SQLSTATE;
exception      when others then v_ErrorCode := SQLSTATE;        v_ErrorMsg  := SQLERRM;        v_Ret       := v_ErrorCode;

 PERFORM pr_write_error_log ();  
END;$$ LANGUAGE 'plpgsql';

SELECT pr_mig_bnft_hist_actn_ldim();
execute the store funtion no error but two tables are the same and didn't delete and/or insert any from one to other;
thank you for looking into it.
v/r,

Bach-Nga

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