Inserted multiple duplicate entry in datagridview

im creating one application where user can be enter there details in datagridview data inserted successfully but when i check again it show me multiple entry has done by one data i pasted here my inserted code and one more query i have iam trying to do update also but its give me No value given for one or more required parameters exception im giving that code also

private void dataGridView1_CellValueChanged(object sender, DataGridViewCellEventArgs e)
        {
 account = dataGridView1.Rows[e.RowIndex].Cells["AccountNumber"].Value.ToString();
            if (account == "")
            {
                account1 = 0;
            }
            else
            {
                account1 = Convert.ToInt32(dataGridView1.Rows[e.RowIndex].Cells["AccountNumber"].Value.ToString());
            }
            if (account1 == 0)
            {



            string connectionString = null;
            connectionString = ConfigurationManager.ConnectionStrings["AccessConnectionString"].ConnectionString;
            con.ConnectionString = connectionString;

            string cmd1 = "insert into Ledger([AccountNumber],[Account],[Date],[Description],[Post_Ref],[Debit],[Credit],[Balance])values(?,?,?,?,?,?,?,?)";
            OleDbCommand cmd = new OleDbCommand(cmd1, con);
            con.Open();
            cmd.CommandType = CommandType.Text;



            int accountNumber;

            bool accountHasValue = int.TryParse(dataGridView1.Rows[e.RowIndex].Cells["AccountNumber"].Value.ToString(), out accountNumber);

            if (accountHasValue)
            {
                cmd.Parameters.AddWithValue("@AccountNumber", accountNumber);
            }
            else
            {
                cmd.Parameters.AddWithValue("@AccountNumber", DBNull.Value);
            }

            string accounts = dataGridView1.Rows[e.RowIndex].Cells["Account"].Value.ToString();
            cmd.Parameters.AddWithValue("@Account", accounts);

            DateTime datetime;
            bool dateTimeHasValue = DateTime.TryParse(dataGridView1.Rows[e.RowIndex].Cells["Date"].Value.ToString(), out datetime);

            if (dateTimeHasValue)
            {
                cmd.Parameters.AddWithValue("@Date", datetime);
            }
            else
            {
                cmd.Parameters.AddWithValue("@Date", DBNull.Value);
            }


            string Description = dataGridView1.Rows[e.RowIndex].Cells["Description"].Value.ToString();
            cmd.Parameters.AddWithValue("@Description", Description);


            string Post_Ref = dataGridView1.Rows[e.RowIndex].Cells["Post_Ref"].Value.ToString();
            cmd.Parameters.AddWithValue("@Post_Ref", Post_Ref);


            int debit;
            bool debitHasValue = Int32.TryParse(dataGridView1.Rows[e.RowIndex].Cells["Debit"].Value.ToString(), out debit);

            if (debitHasValue)
            {
                cmd.Parameters.AddWithValue("@Debit", debit);
            }
            else
            {
                cmd.Parameters.AddWithValue("@Debit", DBNull.Value);
            }


            int Credits;
            bool CreditsHasValue = Int32.TryParse(dataGridView1.Rows[e.RowIndex].Cells["Credit"].Value.ToString(), out Credits);

            if (CreditsHasValue)
            {
                cmd.Parameters.AddWithValue("@Credit", Credits);
            }
            else
            {
                cmd.Parameters.AddWithValue("@Credit", DBNull.Value);
            }

            int Balances;
            bool BalancesHasValue = Int32.TryParse(dataGridView1.Rows[e.RowIndex].Cells["Balance"].Value.ToString(), out Balances);

            if (BalancesHasValue)
            {
                cmd.Parameters.AddWithValue("@Balance", Balances);
            }
            else
            {
                cmd.Parameters.AddWithValue("@Balance", DBNull.Value);
            }


            cmd.ExecuteNonQuery();


            con.Close();


        }

else
         {
          string cmd1 = "update Ledger set [AccountNumber]=?,[Account]=?,[Date]=?,[Description]=?,[Post_Ref]=?,[Debit]=?,[Credit]=?,[Balance]=? where AccountNumber=?";
             OleDbCommand cmd = new OleDbCommand(cmd1, con);
             con.Open();
             cmd.CommandType = CommandType.Text;
             int accountNumber;

             bool accountHasValue = int.TryParse(dataGridView1.Rows[e.RowIndex].Cells["AccountNumber"].Value.ToString(), out accountNumber);

             if (accountHasValue)
             {
                 cmd.Parameters.AddWithValue("@AccountNumber", accountNumber);
             }
             else
             {
                 cmd.Parameters.AddWithValue("@AccountNumber", DBNull.Value);
             }

             string accounts = dataGridView1.Rows[e.RowIndex].Cells["Account"].Value.ToString();
             cmd.Parameters.AddWithValue("@Account", accounts);

             DateTime datetime;
             bool dateTimeHasValue = DateTime.TryParse(dataGridView1.Rows[e.RowIndex].Cells["Date"].Value.ToString(), out datetime);

             if (dateTimeHasValue)
             {
                 cmd.Parameters.AddWithValue("@Date", datetime);
             }
             else
             {
                 cmd.Parameters.AddWithValue("@Date", DBNull.Value);
             }


             string Description = dataGridView1.Rows[e.RowIndex].Cells["Description"].Value.ToString();
             cmd.Parameters.AddWithValue("@Description", Description);


             string Post_Ref = dataGridView1.Rows[e.RowIndex].Cells["Post_Ref"].Value.ToString();
             cmd.Parameters.AddWithValue("@Post_Ref", Post_Ref);


             int debit;
             bool debitHasValue = Int32.TryParse(dataGridView1.Rows[e.RowIndex].Cells["Debit"].Value.ToString(), out debit);

             if (debitHasValue)
             {
                 cmd.Parameters.AddWithValue("@Debit", debit);
             }
             else
             {
                 cmd.Parameters.AddWithValue("@Debit", DBNull.Value);
             }


             int Credits;
             bool CreditsHasValue = Int32.TryParse(dataGridView1.Rows[e.RowIndex].Cells["Credit"].Value.ToString(), out Credits);

             if (CreditsHasValue)
             {
                 cmd.Parameters.AddWithValue("@Credit", Credits);
             }
             else
             {
                 cmd.Parameters.AddWithValue("@Credit", DBNull.Value);
             }

             int Balances;
             bool BalancesHasValue = Int32.TryParse(dataGridView1.Rows[e.RowIndex].Cells["Balance"].Value.ToString(), out Balances);

             if (BalancesHasValue)
             {
                 cmd.Parameters.AddWithValue("@Balance", Balances);
             }
             else
             {
                 cmd.Parameters.AddWithValue("@Balance", DBNull.Value);
             }


             cmd.ExecuteNonQuery();


             con.Close();


        }
}