How do i restrict user from entering duplicate values for vendor's name?

hrh_dash 

Please indent your code consistently, otherwise it is difficult to read.

If you have no code between Else and End If, you don't need Else.

I have removed some inconsistencies from the code, and inserted a question in a comment.

Sub BillingMilestone()
    Dim FileName As String
    Dim CountVendor As Integer
    Dim Count As Integer
    Dim contractbid As String
    Dim sum1 As Long
    Dim sum2 As Long
    Dim sum3 As Long
    Dim sum4 As Long
    Dim ws As Worksheet
    Dim deposit As String
    Dim depositfig As String
    Dim vendor As Range
    Dim cel As Variant
    Dim newVendor As String
    Dim f As Boolean

    Set ws = Sheet1

    FileName = InputBox("Please indicate this file name")
    If FileName = "" Then
        MsgBox ("Macro exited. Click on the button to re-run.")
        Exit Sub
    End If

    ws.Range("A1") = "File Name:"
    ws.Range("B1") = FileName

    CountVendor = InputBox("Please indicate number of vendor(s)")
    If CountVendor = 0 Then
        MsgBox ("You have entered an invalid number. Please click on the clear contents button before re-executing the Macro again")
        Exit Sub
    End If

    ws.Range("A2").Value = "No. of Vendor(s)"
    ws.Range("B2").Value = "Vendor(s) Name"
    ws.Range("C2").Value = "Vendor(s) cost excl GST"
    ws.Range("D2").Value = "Vendor(s) cost incl GST"
    ws.Range("E2").Value = "Vendor(s) payment terms"

    For Count = 1 To CountVendor
        CountVendor = CountVendor + Count
        ws.Range("A" & Count + 2).Value = Count
        f = False
        Do
            newVendor = InputBox("Name of Vendor " & Count)
            If newVendor <> "" Then
                Set vendor = ws.Range("B3:B" & ws.Range("B" & ws.Rows.Count).End(xlUp).Row)
                If Application.WorksheetFunction.CountIf(vendor, newVendor) > 0 Then
                    MsgBox "You have entered a duplicate vendor name entry"
                Else
                    f = True
                End If
            End If
        Loop Until f
        ws.Range("B" & Count + 2).Value = newVendor

        ws.Range("C" & Count + 2).Value = InputBox("Please indicate Vendor " & Count & " amount in SGD (excl GST)")
        ws.Range("C" & Count + 2).NumberFormat = "#,##0.00"
        ws.Range("D" & Count + 2).Value = ws.Range("C" & Count + 2) * 1.07
        ws.Range("D" & Count + 2).NumberFormat = "#,##0.00"
        ws.Range("E" & Count + 2).Value = InputBox("Please indicate Payment Terms for Vendor" & Count & ".")
    Next Count

    sum1 = ws.Cells(ws.Rows.Count, "B").End(xlUp).Row
    sum2 = ws.Cells(ws.Rows.Count, "C").End(xlUp).Row
    sum3 = ws.Cells(ws.Rows.Count, "D").End(xlUp).Row

    ws.Range("A" & sum1 + 1).Value = "Total"

    With ws.Range("C" & sum2 + 1)
        '.NumberFormat = "#,##0.00"
        .Formula = "=SUM(C3:C" & sum2 & ")"
        .Value = .Value
    End With

    ws.Range("C3" & sum2).NumberFormat = "#,##0.00"

    With ws.Range("D" & sum3 + 1)
        '.NumberFormat = "#,##0.00"
        .Formula = "=SUM(D3:D" & sum3 & ")"
        .Value = .Value
    End With

    ' *** Shouldn't this use sum3 instead of sum2 ? ***
    ws.Range("D3" & sum2).NumberFormat = "#,##0.00"

    deposit = InputBox("Deposit required for this tender? Please enter Yes or No.")
    ws.Range("G1").Value = "Deposit Required:"
    ws.Range("H1").Value = deposit
    ws.Range("H1").HorizontalAlignment = xlRight

    If UCase(ws.Range("H1").Value) = "Yes" Then
        ws.Range("G2").Value = "% Deposit of the total contract sum:"
    End If

    sum4 = ws.Cells(ws.Rows.Count, "G").End(xlUp).Row

    ws.Range("G" & sum4 + 1).Value = "Contract Bid (excl GST)"
    ws.Range("G" & sum4 + 2).Value = "Contract Bid (incl GST)"

    contractbid = InputBox("Please indicate contract bid (excl GST).")

    ws.Range("G" & sum4 + 1).Offset(0, 1).Value = contractbid
    ws.Range("G" & sum4 + 1).Offset(0, 1).NumberFormat = "#,##0.00"

    ws.Range("G" & sum4 + 2).Offset(0, 1).Value = contractbid * 1.07
    ws.Range("G" & sum4 + 2).Offset(0, 1).NumberFormat = "#,##0.00"
        
    If UCase(ws.Range("H1").Value) = "Yes" Then
        depositfig = InputBox("Please indicate deposit % of the total contract sum. For eg, 5% deposit, please enter as 5.")
        ws.Range("H2").Value = (ws.Range("G" & sum4 + 2).Offset(0, 1) / 100) * depositfig
        ws.Range("H2").NumberFormat = "#,##0.00"
    End If

    Call contracttenure
    Call findlastrow
    Call amrtbilling
    Call Alignment
End Sub