Simple SUM filter problem driving me crazy

Dear power friends, 

I have a regular monthly CALENDAR_TABLE with the typical content

DATE
01/01/2018
02/01/2018
03/01/2018
(...)

linked to a SALES_TABLES by a date column in the same format (MM / 01/2018)
I need to sum the sales for only the last month of the selected date range. For example: if I select 01/01/2018 - 03/01/2018,  I will get the sum of sales only for month 03.

I've tryed:

1) create a measure called dMaxDateCalendar = LASTDATE(CALENDAR_TABLE[date])

and

2) the following measure

CALCULATE (
         SUM (SALES_TABLES [sales]);
         FILTER (SALES_TABLE;
                          SALES_TABLES[data] = [dMaxDateCalendar])
         )

But it returned de sum of all date range

than I've tryed:

3) SUMX(FILTER(SALES_TABLE;

SALES_TABLE[date]=[dMaxDataCalendario]);

SALES_TABLES [sales])

 but it returned, again, de sum of all date range.

What am I doing wrong?

Thanks,