Check if value exists, if not add to list

My goal: Check if value exists, if the value not exists add at the end of column A. If the value exists skip the ID and check the next value.

Actual result: The IDs will be added at the end of line A neverthelesss if the value exists or not. Therfore I get duplicates.

I tried with "if" but I get an error.

My coding:

Option Explicit


Sub ExposeID()

Dim browser As Object   'Aufnehmen der verwendeten Instanz des Browsers (Internet Explorer)
Dim knotenAst As Object 'Aufnehmen einer HTML Struktur aus dem Browser Dokument
Dim n As Integer
Dim url As String       'Aufnehmen der auszulesenden Adresse

Dim ExposeID As String
Dim letztezeile As Integer
Dim nodeList As Object, i As Long

Set browser = CreateObject("internetexplorer.application")
    browser.Visible = False

For n = 0 To 1

    url = "https://www.immobilienscout24.de/Suche/de/niedersachsen/oldenburg-oldenburg/haus-kaufen?pagenumber=" & n + 1
    browser.navigate url
    Do Until browser.readyState = 4: DoEvents: Loop

    letztezeile = ActiveSheet.Cells(Rows.Count, 1).End(xlUp).Row

Set nodeList = browser.document.querySelectorAll(".result-list__listing[data-id]")

For i = 0 To nodeList.Length - 1

    ''' HERE IS THE PROBLEM '''
    If nodeList.Item(i).getAttribute("data-id") <> Cells.Range("A:A") Then
       Cells(letztezeile + i + 1, 1) = nodeList.Item(i).getAttribute("data-id")

    Else

    End If

Next i

Next n

Set nodeList = Nothing
browser.Quit

End Sub