Copying workbook to main workbook

I am trying to create a macro that will copy the data thats in a .csv file
and then copy it to a .xls (Excel Workbook) file, I wrote some code for it,
but it's only copying the .xls files and when I change the fileformat to .csv
it doesn't work at all, my code can be seen below:

Sub CopyRange()
Dim basebook As Workbook
Dim mybook As Workbook
Dim sourceRange As Range
Dim destrange As Range
Dim rnum As Long
Dim i As Long
Dim a As Long
Application.ScreenUpdating = False
With Application.FileSearch
.NewSearch
.LookIn = "S:\IndexServices\Alex\Test CDS\CMA Data\CMA Files"
.SearchSubFolders = False
.FileType = msoFileTypeExcelWorkbooks
If .Execute() > 0 Then
Set basebook = ThisWorkbook
rnum = 1
For i = 1 To .FoundFiles.Count
Set mybook = Workbooks.Open(.FoundFiles(i))
Set sourceRange = mybook.Worksheets(1).Range("a1:M600")
a = sourceRange.Rows.Count
Set destrange = basebook.Worksheets(2).Cells(rnum, 1)
sourceRange.Copy destrange
mybook.Close
rnum = i * a + 1
Next i
End If
End With
Application.ScreenUpdating = True
End Sub


I also want it so that when it is copying to the main workbook, it copy's
after the last data that has been entered, meaning I don't want the data
thats already on the sheet to be erased, but for it to just be added to the
data thats already on the main workbook, does anyone know of a way to do this?