Sort by short month name(Colum Name)in the Tablix

I want to sort by short month name (Jan , Feb.....Dec) in my Tablix .... I am able to sort in the stored procedure bind to the report dataset... But in the report , it won't  work IN THE TABLIX..
Please provide me the expression to achieve this....... Please see the attached report which is not sorted by short month name and also the query results of the stored procedure



Query(Stored procedure) bind to the Data SET :

SELECT     COUNT(INV_NUMBER) AS Invoices_Processed,
               NWO_SHORT_CODE,
              INV_BILLING_PERIOD_MONTH ,
               CASE INV_BILLING_PERIOD_MONTH
                                      WHEN 1 THEN 'Jan'
                                      WHEN 2 THEN 'Feb'
                                      WHEN 3 THEN 'Mar'
                                      WHEN 4 THEN 'Apr'
                                      WHEN 5 THEN 'May'
                                      WHEN 6 THEN 'Jun'
                                      WHEN 7 THEN 'Jul'
                                      WHEN 8 THEN 'Aug'
                                      WHEN 9 THEN 'Sep'
                                      WHEN 10 THEN 'Oct'
                                      WHEN 11 THEN 'Nov'
                                      WHEN 12 THEN 'Dec'
                                      ELSE 'Unknown'
                                      END AS Billing_Month
FROM    INVOICE INV INNER JOIN INVOICE_TYPE ITP ON INV.INV_TYPE_ID = ITP.INV_TYPE_ID
WHERE   ITP.INV_CLASSIFICATION_CODE = 'TND' AND (NWO_SHORT_CODE IN (SELECT CODE FROM DNO))
AND  INV_BILLING_PERIOD_MONTH   BETWEEN @Billing_Month_From  AND @Billing_Month_To
AND   INV_BILLING_PERIOD_YEAR = @Billing_Period_Year
GROUP BY NWO_SHORT_CODE, INV_BILLING_PERIOD_MONTH ,INV_BILLING_PERIOD_YEAR, INV_CLASSIFICATION_CODE
ORDER BY INV_BILLING_PERIOD_MONTH ASC







   
Query-Results.txt
Report.docx