Forms Data Controls :: Load Values From Database To Dropdown Before AddQuotenumber Button?

I have Dropdown for Quotenumber(auto increment ).i have created a function to retreive the data from database.data loading into dropdown. when i click on Addquotenumer button the new quotenumber generated and same loading into dropdown but 2 set of Quotenumbers are displaying rather than singleset, i debudded the code the reason was i have called this function twice one is form load and another one in AddQuotenumber button event,both should manadetory as per my requirement. how can un load this dropdown before AddQuotenumber button

Function to retreive data to dropdown
Public Sub retriveDataToDropDown()
Try
Dim connectionString As String = "Database=fabdb;" & "Data Source=localhost;" & "User Id=root;Password=pacvision"
Dim query As String = "SELECT QuoteNumber FROM quotes"
Dim connection As New MySqlConnection(connectionString)
Dim da As New MySqlDataAdapter(query, connection)
Dim ds As New DataSet()
If da.Fill(ds) Then
DDQuote.DataSource = ds.Tables(0)
DDQuote.DataTextField = "QuoteNumber"
DDQuote.DataBind()
'DDQuote.Items.Insert(0, New ListItem("Select", "Default value"))
End If
connection.Close()
Catch ex As Exception
'Console.WriteLine(ex.Message)
End Try
End Sub
AddquoteNumber button code
Protected Sub btnAQ_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnAQ.Click
Dim connectionString As String = "Database=fabdb;" & "Data Source=localhost;" & "User Id=root;Password=pacvision"
Dim rowsEffected As Integer = 0
Dim Query As String = ""
Dim connection As New MySqlConnection(connectionString)
'Dim cmd As New MySqlCommand(Query, connection)
connection.Open()
Query = "insert into Quotes(query follows...................)
retriveDataToDropDown()
retriveDataToDataGrid()
connection.Close()
End Sub