How to update invoice table in VB.Net and MS Access 2007

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VB

Hello everyone My name is Sarfaraz and I am stuck with the following problem in my project which I am developing in VB.Net and MS Access 2007.
I am actually having a table called INVOICE with field name as ac_no,credit,debit and dated. I am adding a new record in this table if the account number ac_no is not already available in the invoice table but if the ac_no is already available I just wanted to update the credit and debit fields with the amount credited and debited by entering values in two text boxes txtcredit and txtdebit but i am getting an error like data type mismatch in creteria expression.
I want like if credit field has 1000 and debit has 500 for a record having ac_no 112 then i want the values to be like 2000 for credit field and 1000 for debit field if i enter 1000 and 500 in txtcredit and txtdebit textboxes.

My code is as below:

Private Sub btnok_Click(sender As Object, e As EventArgs) Handles btnok.Click
        If Con.State = ConnectionState.Open Then
            Con.Close()
        End If
        Dim query As String
        Dim credit, debit As Double
        Dim dt As DateTime
        dt = dtpicker1.Value.Date
        credit = CDbl(txtcredit.Text)
        debit = CDbl(txtdebit.Text)
        query = "update invoice set [credit]='" & CDbl(txtcredit.Text) & " ' ,[debit]= ' " & CDbl(txtdebit.Text) & " ',[dated]=' " & dtpicker1.Value.Date & " ' where [ac_no]= ' " & Integer.Parse(txtacno.Text) & " '"
        Dim cmd = New OleDbCommand
        Con.Open()
        cmd.CommandText = query
        cmd.Connection = Con
        cmd.ExecuteNonQuery()
        Con.Close()
        MsgBox("Successfully  edited ")
    End Sub

Thank you