Changing A Csv Format To Xls And Saving/closing

I am trying to write a macro/program that will save a csv activeworkbook in xls and close it.

The workbook will always be a different name.

The files do not have an extension upon download and formatting.
ie stm0107 (Then they need to be saved as xls. Which is done manually at this time.)

Below are some trial and error attemtps. Thank you for your suggestions.

Sub CloseWorkbook()
Dim Filename As String
'Filename = Workbook.Name
MsgBox (ActiveWorkbook.Name)
Filename = ActiveWorkbook.Name
ActiveWorkbook.SaveAs Filename = ActiveWorkbook.Name(".xls")

'Filechange = Replace(Filename, "", "xls")
Application.DisplayAlerts = False
ActiveWorkbook.Save
Application.DisplayAlerts = True
ActiveWorkbook.Close Saved = True
End Sub