Called stored procedure runs and update table 2 times instead of once

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SQL-Server-2008R2

Calling Stored procedure
--------------------------

IF @ZEQUALPAY='SIMPLE'
BEGIN

WHILE @STARTPERIOD<=@ENDPERIOD
BEGIN

SET @CMONTH = @ZPERIOD
SET @CYEAR = @ZYEAR

SET @STARTPERIOD = CONVERT(NVARCHAR,@ZCCYR)+ Right('00' + Convert(varchar(10),@ZCCMTH), 2)

EXEC [dbo].[sp_simple] @ZIDNO,@ZLOANUMBER,@CMONTH,@CYEAR,@RETURN

IF @ZPERIOD = 12
BEGIN
SET @ZCCMTH = 1
SET @ZCCYR = @ZYEAR+1
END
ELSE
IF @ZPERIOD <> 12
BEGIN
SET @ZCCMTH =@ZPERIOD+1
SET @ZCCYR =@ZYEAR
END

SET @ZPERIOD = @ZCCMTH
SET @ZYEAR = @ZCCYR

SET @STARTPERIOD = CONVERT(NVARCHAR,@ZCCYR)+ Right('00' + Convert(varchar(10),@ZCCMTH), 2)


END
END














Called Stored Procedure
------------------------
------------------------

ALTER PROCEDURE [dbo].[sp_simple]
	(
	@ZIDNO          Varchar(20),
	@ZLOANUMBER     Varchar(20),
	@CMONTH         Int,
	@CYEAR          Int,
	@RETURN		   varchar(4) OUTPUT     
	)
	AS

	BEGIN

	DECLARE @AIDNO       varchar(20),
	@ALOANTYPE   varchar(20),
	@ADEDUCT     money,
	@ATERM_START DECIMAL(22,10),
	@ACCNT       smallint ,
	@BINT_NO     varchar(20),
	@BINT_NAME   varchar(50),
	@BRATES     DECIMAL(22,10)
  
	SELECT @AIDNO    = A.IDNO        ,
	@ALOANTYPE      =  A.LOANTYPE   ,
	@ADEDUCT        =  A.DEDUCT     ,
	@AOUTSTAND      =  A.OUTSTAND   ,
	@ACOMPCOUNT     =  A.COMPCOUNT  ,
	@AINT_NO        =  A.INT_NO     ,
	@ACCNT          =  A.CCNT       ,
	@ASACCRUED      =  A.SACCRUED ,
	@ANUMDAYS       =  A.NUMDAYS  ,
	@BINT_NO         =  B.INT_NO   ,
	@BINT_NAME       =  B.INT_NAME   ,
	@BRATES          =  B.RATES
	FROM LOANS A JOIN INTEREST B
	ON A.INT_NO = B.INT_NO WHERE  REPAY_MODE='SIMPLE INTEREST' AND COMPCOUNT>=1
	AND A.IDNO=@ZIDNO AND A.LOANUMBER=@ZLOANUMBER
  
		 
	SET @ACCNT = @ACCNT+1	
		
		
		IF @APAY_TYPE  ='MONTHLY'
		BEGIN		
		
		IF @AMORAT_MTHS=0 AND @AMORATORIUM=0 AND @ACCNT <=@ATERM_START

Problem
--------
@RESULTS

1. YES

Return Value

1. 0
The program runs ahead hence the calculation of

SET @ACCNT = @ACCNT+1

is done about three times before the condition below is reached,
thereby defeating the condition.


SET @ACCNT is in 0 from the table how ever before it gets to where the
condition for it to be tested it is reading 3.



IF @AMORAT_MTHS=0 AND @AMORATORIUM=0 AND @ACCNT <=@ATERM_START


How do I handle the @RETURN so that the flow of the program will be orderly.


Thanks

What I have tried:

There are no examples. This is a peculiar problem