DECLARE @dt_from    DATETIME        =   '2016-01-01';
DECLARE @dt_to      DATETIME        =   '2016-02-01';
DECLARE @acc        VARCHAR(256)    =   '1-AAA';


SELECT
     [Month_Name]   =   DATENAME(MONTH, [agg_data].[dt]) + SPACE(1) + CAST(DATEPART(YEAR, [agg_data].[dt]) AS VARCHAR(4))
--  ,[Month]        =   [agg_data].[dt]
    ,[Invoice_Amt]  =   [agg_data].[amount_inv]
    ,[Payment_Amt]  =   [agg_data].[amount_pmt]
FROM
    (
        SELECT
              [dt]          =   ISNULL([i].[dt], [p].[dt])
             ,[amount_inv]  =   ISNULL([i].[amount], 0)
             ,[amount_pmt]  =   ISNULL([p].[amount], 0)
             ,[acc]         =   ISNULL([i].[acc], [p].[acc])
        FROM
            (
                SELECT
                     [acc]      =   [account]
                    ,[dt]       =   DATEFROMPARTS(YEAR([trans_date]), MONTH([trans_date]), 1)
                    ,[amount]   =   SUM([amount])
                FROM
                    [invoice]
                GROUP BY
                     DATEFROMPARTS(YEAR([trans_date]), MONTH([trans_date]), 1)
                    ,[account]
            )   AS  [i]
        FULL JOIN
            (
                SELECT
                     [acc]      =   [account]
                    ,[dt]       =   DATEFROMPARTS(YEAR([payment_date]), MONTH([payment_date]), 1)
                    ,[amount]   =   SUM([amount])
                FROM
                    [payment]
                GROUP BY
                     DATEFROMPARTS(YEAR([payment_date]), MONTH([payment_date]), 1)
                    ,[account]
            )   AS  [p]
        ON
                [i].[acc]   =   [p].[acc]
            AND [i].[dt]    =   [p].[dt]
    )   AS  [agg_data]
WHERE
        [dt]    BETWEEN @dt_from AND @dt_to
    AND [acc]   =       @acc
ORDER BY
     [dt] ASC;