What I understood from what you shared, in your calendar table the month level is actually a date and your hierarchy is year/month/date and that doesn't filter the whole month it filters only the single value of the date and because you have date on rows, Excel queries all the dates and the Pivot cache ends up showing the previous grand total.

You need to create a month column for the month level instead of the date and sort it by the YearMonthNumber :

YearMonthText = FORMAT([Date], "yyyy/MM")
YearMonthNumber = YEAR([Date] * 100 + MONTH[Date]

and build your hierarchy Year + YearMonthText + Date