Countif in VBA returns wrong result.

I have a list of date in A3:A13 and 1 date in C1
All dates are formatted as dd/mm/yyy
I try to countif as follow:
=COUNTIF(A3:A13,"<="&C1)
it is OK
but try with VBA:

Sub a()
Dim adate As Range
Dim n As Long
Set adate = Range("A3:A13")
n = WorksheetFunction.CountIf(ngay, "<=" & Range("C1"))
Debug.Print n
End Sub

it returns wrong result
See attachment.
Anybody can help?