Why error messages are not returning code behind in my Stored Procedure ?

ALTER PROCEDURE [dbo].[VALIDATE_MASS_EMPDATA_UPDATION]    
(    
 @corporateId    VARCHAR(20),     
 @empId                  VARCHAR(20),     
 @citizenId                  VARCHAR(15),    
    @cardNo      VARCHAR(19),    
 @p_error_code  INT    OUTPUT,      
 @p_error_msg  VARCHAR(1000) OUTPUT 
   
)    
AS    
BEGIN    
 SET  NOCOUNT ON    
 DECLARE @error    VARCHAR(40)    
DECLARE @C3EMPREGID BIGINT    
SET @C3EMPREGID=0    
 --Added by Alex on Feb 7,2014 to retrieve correct card no as masked is now passed as parameter in Excel    
--  SELECT @C3EMPREGID=C3EMPREGID FROM EMPLOYEE     
--  WHERE EmpId=@empId     
--  AND CitizenId=@citizenId      
--  AND right(rtrim(@cardNo),4)=right(rtrim(CardNo),4)    
--  AND CorporateId=@corporateId     
--  AND Isdeleted=0      
       
--print @C3EMPREGID     
--Added by Alex in where clause with primary key @C3EMPREGID     
   IF Not EXISTS (SELECT EmpId FROM dbo.Employee WHERE EmpId=@empId and CorporateId=@corporateId )  
   BEGIN  
   SET @p_error_code='500'  
    IF(@p_error_msg !='')
   SET @p_error_msg = @p_error_msg 
   SET @p_error_msg=@p_error_msg + 'Invalid employee. :'  
     
   --return(1)  
   END  
   IF not EXISTS (SELECT CardNo FROM dbo.Employee WHERE EmpId=@empId and CorporateId=@corporateId and right(rtrim(@cardNo),4)=right(rtrim(CardNo),4))  
   BEGIN  
   SET @p_error_code='200'  
   IF(@p_error_msg !='')
   SET @p_error_msg = @p_error_msg
   SET @p_error_msg = @p_error_msg + ' Invalid Card Number : '  
   --return(1)  
   END    
   
   --Added by Alex for Invalid Citizen Id in where clause with Citizen Id    
   IF Not EXISTS (SELECT CitizenId FROM dbo.Employee WHERE EmpId=@empId and CorporateId=@corporateId  and CitizenId= @citizenId)    
   BEGIN    
  
   SET @p_error_code='300'    
      IF(@p_error_msg !='')
   SET @p_error_msg = @p_error_msg 
   SET @p_error_msg = @p_error_msg + ' Invalid Citizen Id. :'    
   --return(1)     
   END    
     
     
     if @p_error_code<>'0'
      BEGIN    
     --print @p_error_msg
     SET @p_error_msg =@p_error_msg
     return(1)
         
   END