Stop insert duplicated records in database in C#

private void SaveData()
        {
            String connstring = ConfigurationManager.ConnectionStrings["FincorpData"].ConnectionString;
            string cmdstring = "insert into customer (RollNumber, Name, FatherName, Address, Address1, MobileNo, SecMobileNo, City, District, State, PinCode, Remark) VALUES (@RollNumber, @Name, @FatherName, @Address, @Address1, @MobileNo, @SecMobileNo, @City, @District, @State, @PinCode, @Remark)";
          
            using (OleDbConnection con = new OleDbConnection(connstring))
            {
                using (OleDbCommand cmd = new OleDbCommand(cmdstring, con))
                {
                    con.Open();

                    cmd.Parameters.AddWithValue("@RollNumber", textBoxRollNumber.Text);
                    cmd.Parameters.AddWithValue("@Name", txtName.Text);
                    cmd.Parameters.AddWithValue("@FatherName", txtFatherName.Text);
                    cmd.Parameters.AddWithValue("@Address", txtAddress.Text);
                    cmd.Parameters.AddWithValue("@Address1", txtAddress1.Text);
                    cmd.Parameters.AddWithValue("@MobileNo", txtMobileNo.Text);
                    cmd.Parameters.AddWithValue("@SecMobileNo", txtSecMobileno.Text);
                    cmd.Parameters.AddWithValue("@City", txtCity.Text);
                    cmd.Parameters.AddWithValue("@District", txtDistrict.Text);
                    cmd.Parameters.AddWithValue("@State", txtState.Text);
                    cmd.Parameters.AddWithValue("@PinCode", txtPinCode.Text);
                    cmd.Parameters.AddWithValue("@Remark", txtRemark.Text);

                    cmd.ExecuteNonQuery();
                    MessageBox.Show("Recourd is saved", "Success", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    con.Close();
                }   
            }
        }