How to avoid duplication in Excel VBA Macro - excel

Question

Beginner here and I managed to modify a code to extract data from a sheet and copy and paste them to other sheets. Problem is when I click run Macro or the button assigned to the Macro, it is duplicating rows again. Please help me to avoid the duplication.
TIA
Sub UpdateHistory()
Dim wsData As Worksheet, wsCostCode As Worksheet
Dim LastRow As Long, NextRow As Long, i As Long
Dim CostCode As String
Dim Company As String
Dim Invoice As String
Dim Price As Double
Application.ScreenUpdating = False
Set wsData = Sheets("Signed Invoices")
LastRow = wsData.Cells(Rows.Count, 1).End(xlUp).Row
For i = 2 To LastRow
CostCode = wsData.Range("A" & i).Value
Company = wsData.Range("B" & i).Value
Invoice = wsData.Range("C" & i).Value
Total = wsData.Range("D" & i).Value
If WorksheetExists(CostCode) = True Then
Set wsCostCode = Sheets(CostCode)
NextRow = wsCostCode.Cells(Rows.Count, 1).End(xlUp).Row + 1
wsCostCode.Range("A" & NextRow).Value = CostCode
wsCostCode.Range("B" & NextRow).Value = Company
wsCostCode.Range("C" & NextRow).Value = Invoice
wsCostCode.Range("D" & NextRow).Value = Total
Else
wsData.Range("A1:D1").Copy
Worksheets.Add(After:=Sheets(Sheets.Count)).Name = CostCode
ActiveSheet.Cells(1, 1).PasteSpecial
ActiveSheet.Range("A2").Value = CostCode
ActiveSheet.Range("B2").Value = Company
ActiveSheet.Range("C2").Value = Invoice
ActiveSheet.Range("D2").Value = Total
End If
Next
Application.CutCopyMode = False
Sheets("Signed Invoices").Select
Application.ScreenUpdating = True
End Sub
Function WorksheetExists(shtName As String, Optional wb As Workbook) As Boolean
Dim sht As Worksheet
If wb Is Nothing Then Set wb = ThisWorkbook
On Error Resume Next
Set sht = wb.Sheets(shtName)
On Error GoTo 0
WorksheetExists = Not sht Is Nothing
End Function

Answer 1

When you find that your code isn't doing what you expect, try stepping through it line-by-line and see exactly where and when it goes wrong. You can do this by pressing F8 while your cursor is anywhere in your macro. I also recommend commenting out Application.ScreenUpdating = False until your code is working as expected. Otherwise, following the code's behavior can become difficult when the code is supposed to write things to worksheets.
You've found that your code is duplicating entries. Let's check all places in your macro that write data to the sheet. There is only one place: inside your For i = 2 to LastRow loop. Because you have set up a loop, you are expecting (or at least preparing) for this block of code to run more than once. The next question should be, why is the data not changing between two iterations like you're expecting?
Check that Else block of code. It seems like you copy the headers, add a new sheet, and then use the ActiveSheet to specify which sheet to write the data. Is ActiveSheet the sheet you think it is? (Very easy to verify with line-by-line debugging.) If you really want to use ActiveSheet, make sure the sheet you expect to be active is active with Worksheets(Worksheets.Count).Activate. This will activate the last worksheet, which is where you want to write your data.
Try stepping line-by-line through your code and see if this is correct before modifying your code.