Subtracting amount ONLY IF the amount is at certain value in VB.NET using Access database

the following are the codes. I am ONLY allowed to withdraw/subtract a value ONLY IF the balance amount(after subtracting) in the database is above certain amount . Example: If balance amount in database >= 100 after subtracting, then subtraction successful. Else If balance amount in database <= 100, then subtraction denied.

         If IsNumeric(accountnotxt.Text.ToString) And IsNumeric(amounttxt.Text.ToString) = True Then

        cmdsearch.CommandText = "SELECT * FROM [Current_Account] WHERE [AccountNo] =  " & accountnotxt.Text
        cmdupdate.CommandType = CommandType.Text
        cmdsearch.Connection = cnnoledb

        Dim read As OleDbDataReader = cmdsearch.ExecuteReader()
        Dim withdrawamt As Decimal

        withdrawamt = withdrawamt - amounttxt.Text >= 100

If read.Read = True Then withdrawamt = read(2).ToString ' this is the column of Amount in database

        If read.Read = True Then
            withdrawamt = read(2).ToString  
            cmdupdate.CommandText = "UPDATE [Current_Account] SET [Amount] = " & withdrawamt & " WHERE [AccountNo] =" & accountnotxt.Text.ToString & ";"
            cmdupdate.CommandType = CommandType.Text
            cmdupdate.Connection = cnnoledb
            cmdupdate.ExecuteNonQuery()

            MsgBox(" Successfully withdrawn from account " + accountnotxt.Text)
        Else
            MsgBox("Minimum of 100 must be available in your account.")
        End If
        read.Close()
    Else
        MsgBox(" Please enter valid information. ")

The program did not crash and no changes in the database than the MsgBox that showed up.

Thanks in advance !