ORA-01422: exact fetch returns more than requested number of rows

Hi i have the following function am geting this error when i pass value

CREATE OR REPLACE FUNCTION GEN_CURRENT_AccNo (vsInput VARCHAR2)
   RETURN number
   

IS
   wrk_sin number;


   lsNSN    VARCHAR2 (255);
 
   lnRow    ITEM_BASIC%ROWTYPE;
   lnCode   IITEM_BASIC.SIN%TYPE;
   lnAccnr    ITEM_BASIC.SIN%TYPE;

   c_cnt_acc number(10);





BEGIN
   



  SELECT *
     INTO lnRow
     FROM (SELECT *
             FROM ITEM_BASIC a
            where a.ITM_CODE = regexp_replace(vsInput,'[^[:digit:]]')
           UNION ALL
           SELECT *
             FROM ITEM_BASIC a
            WHERE ITM_CB||ITM_NR||ITM_NAME = vsInput)
    WHERE ROWNUM <= 1;



   IF lnRow.item_type = '9' then
  
      
     SELECT SIN
        INTO lnCode
        FROM (    SELECT *
                    FROM ITEM_DATA
              START WITH ITM_CODE = lnRow.ITM_CODE
              CONNECT BY NOCYCLE PRIOR TO_CODE = ITM_CODE)            
       WHERE TO_CODE IS NULL;

      

   ELSE
      
    lnAccnr := lnRow.ITM_CODE;
 
   END IF;


   RETURN lnAccnr;

  

EXCEPTION
   WHEN OTHERS
   THEN
      raise_application_error (-20001, SQLERRM);

END;

CREATE TABLE ITEM_DATA
   (ITM_CODE NUMBER(11,0) primary key, 
    accountNr varchar(20),--accountNr=ITM_CB||ITM_NR||ITM_NAME
	TO_CODE NUMBER(11,0), 
	accountNrTo varchar(20),
	ITEM_VERSION VARCHAR2(20 BYTE), 
	CONSTRAINT TO_CODE_UQ UNIQUE (ITM_CODE, TO_CODE));
	 
	 
CREATE TABLE ITEM_BASIC 
   (ITM_CODE NUMBER(11,0), 
	ITM_NAME VARCHAR2(23 BYTE), 
	ITM_CB VARCHAR2(50 BYTE), 
	ITM_NR VARCHAR2(20 BYTE), 
	item_type varchar(2),
	CONSTRAINT IM_CODE_PK PRIMARY KEY (ITM_CODE);
    CONSTRAINT IT_CODE_FK FOREIGN KEY (ITM_CODE)
	REFERENCES ITEM_DATA1 (ITM_CODE) ENABLE;	

in database they will be like this


ITM_CODE   accountNr       TO_CODE     accountNrTo
20751411   3120LB1433679   20751411    3120180573151
20751411   3120180573151   159960150   3120144348210


i what my function to return 159960150 either user pass 20751411 or 3120LB1433679

am in 11g