Filter a DateTime field for year,month and day in excel pivot

I'm using EPPlus to create Excel reports. Now i'm trying to create a Pivot with a DateTime PageField, so that the user can filter the period he want to see by himself. But although i can filter this for year,month or days in the according d开发者_如何学Cata worksheet by default, i don't get it working in the Pivot.

Here is what i have:

Dim wsPivot = excel.Workbook.Worksheets.Add("Pivot")
Dim wsData = excel.Workbook.Worksheets.Add("Data")
Dim source = workSheet.GetDataSource
wsData.Cells("A1").LoadFromDataTable(source, True, OfficeOpenXml.Table.TableStyles.Medium6)
For Each col As DataColumn In source.Columns
    If col.DataType = GetType(Date) Then
        Dim colNumber = col.Ordinal + 1
        Dim range = wsData.Cells(1, colNumber, source.Rows.Count, colNumber)
        range.Style.Numberformat.Format = "dd.mm.yyyy"
   End If
Next
Dim dataRange = wsData.Cells(wsData.Dimension.Address.ToString())
dataRange.AutoFitColumns()
Dim pivotTable = wsPivot.PivotTables.Add(wsPivot.Cells("A3"), dataRange, "Open Contacts")
pivotTable.PageFields.Add(pivotTable.Fields("OwnedAt")) '** this is the date column i want to group **'
pivotTable.PageFields.Add(pivotTable.Fields("Owner"))
pivotTable.RowFields.Add(pivotTable.Fields("Country"))
pivotTable.ColumnFields.Add(pivotTable.Fields("Status"))
pivotTable.DataFields.Add(pivotTable.Fields("Count"))

It's only possible to select datetime values from the list including hours and minutes and not to group by month f.e.(see picture below).

Here is the filter-list from the data-worksheet. How to get this in pivot?

Thank you in advance.

Note: I've also asked this on codeplex without success. Maybe someone else can help even if he has no experiences with EPPlus but knows similar issues with other libraries. I could split the DateTime values into separate columns per sql(year,month,day). But i'm afraid that the pivot will get more confusing with so many fields( i also would have to split the other date fields). Even with no experiences at all in programatically generating pivots, what would experienced excel users(i'm not) recommend?

The reason why excel could not group by my date-field neither in PageField nor in RowField was because there was one unformatted row in the data sheet. The following lines cause this issue(see complete code in my question):

Dim range = wsData.Cells(1, colNumber, source.Rows.Count, colNumber)
range.Style.Numberformat.Format = "dd.mm.yyyy"

The parameters in the range's Cells-Method are:

1. From-Row 2. From-Column 3. To-Row 4. To-Column

Because LoadFromDataTable loaded the DataTable with the Colums' names as header, the last row kept unformatted, therefore the pivot cannot group the date.

So this fixed it:

Dim range = wsData.Cells(2, colNumber, source.Rows.Count + 1, colNumber)