insert all values

//FROM INSIDE SQL CONFIG CLASS !!!!!
 public void InsertMember(string firstname, string lastname, string phonenumber, string dob, string postcode, int memstatus, string memregdate)
        {
            SqlConnection FelicityConn = new SqlConnection(ConnectionString);

            SqlCommand Insertmembercmd = new SqlCommand();


            //INSERT STATEMENT USING PREDEFINED STRING VARIABLES

            Insertmembercmd.CommandText = string.Format("INSERT INTO  MemberTable (MemFirstname, MemLastname, MemPhonenumber, MemDOB, MemPostcode, MemStatus, MemRegDate) VALUES ('{0}','{1}','{2}','{3}','{4}','{5}','{6}')", firstname,
            lastname, phonenumber, dob, postcode, memstatus, memregdate, FelicityConn);


            Insertmembercmd.Parameters.AddWithValue("@MemFirstname", firstname.ToUpper());//PARAMETER 0
            Insertmembercmd.Parameters.AddWithValue("@MemLastname", lastname.ToUpper());//PARAMETER 1
            Insertmembercmd.Parameters.AddWithValue("@MemPhonenumber", phonenumber);//PARAMETER 2
            Insertmembercmd.Parameters.AddWithValue("@MemDOB", dob);//PARAMETER 3
            Insertmembercmd.Parameters.AddWithValue("@MemPostcode", postcode);//PARAMETER 4
            Insertmembercmd.Parameters.AddWithValue("@MemStatus", memstatus);//PARAMETER 5
            Insertmembercmd.Parameters.AddWithValue("@MemRegDate", memregdate);//PARAMETER 6



            /*OPEN THE CONNECTION
            EXECUTE THE INSERT QUERY
            CLOSE CONNECTION*/

            Insertmembercmd.Connection = FelicityConn;
            FelicityConn.Open();
            Insertmembercmd.ExecuteNonQuery(); //EXECUTE THE INSERT STATEMENT COMMAND
            FelicityConn.Close();

            //END OF METHOD

        }

//FROM THE FORM OF THE INSERT BUTTON
 private void BtnAddMem_Click(object sender, EventArgs e)
        {
            DateTime RegDate = DateTime.Parse(RegMemDate.ToString());
            DateTime DOB = DateTime.Parse(RegMemDate.ToString());

            if (TxtFirstName.Text != "" && TxtLastName.Text != "" && TxtPhoneNumber.Text != "" && TxtPostCode.Text != "" && DobMem.Text != "" && RegMemDate.Text != "")
             {

                 SQLConfig sqlclass = new SQLConfig();
                 if (sqlclass.InsertMember(TxtFirstName.Text.ToString(),TxtLastName.Text.ToString(), TxtPhoneNumber.Text.ToString(),TxtPostCode.Text.ToString(), DOB.ToString(), RegDate.ToString()))
                 {
                     MessageBox.Show("Registered a new member" + TxtFirstName);
                 }

             }