Match data in 2 columns and return all results from a 3rd to a single cell

Hi all,
I have a spreadsheet that has 3 columns of data. I need to match results from 2 of the columns and return all the results from the corresponding 3rd column into a single cell. I have found some code that does this for a single search but I don't know how to expand this to search in an additional column. This code is below. Please could someone help?

'Multiple lookup and no repeat function, finds and lists all unique numbers in row form

Function MultipleLookupNoRept(Lookupvalue As String, LookupRange As Range, ColumnNumber As Integer)
    Dim xDic As New Dictionary
    Dim xRows As Long
    Dim xStr As String
    Dim i As Long
    On Error Resume Next
    xRows = LookupRange.Rows.Count
    For i = 1 To xRows
        If LookupRange.Columns(1).Cells(i).Value = Lookupvalue Then
            xDic.Add LookupRange.Columns(ColumnNumber).Cells(i).Value, ""
        End If
    Next
    xStr = ""
    MultipleLookupNoRept = xStr
    If xDic.Count > 0 Then
        For i = 0 To xDic.Count - 1
            xStr = xStr & xDic.Keys(i) & ","
        Next
        MultipleLookupNoRept = Left(xStr, Len(xStr) - 1)
    End If
End Function