How to get selected text and selected value of comboBox in C#

DATA BIND HERE 

public VolunteerSettings()
{
  InitializeComponent();
  GetVolunteer();           
}

private void GetVolunteer()
{
 ConfigurationDAL c = new ConfigurationDAL();
 DataTable dt = new DataTable();
 drp_Volunteeer.DataSource = c.GetVolunteerList().Tables[0];
 drp_Volunteeer.ValueMember = "volunteerid";
 drp_Volunteeer.DisplayMember = "volunteername";           
}

 volunteerid : 12008 Direct Data Get

I Will try drp_volunteer this method data can't get 

  private void drp_Volunteeer_SelectedIndexChanged(object sender, EventArgs e)
        {
          
            ConfigurationDAL dal = new ConfigurationDAL();
            DataTable dt = new DataTable();
            dt = dal.FetchVolunteerDetails(volunteerID: 12008).Tables[0];

            foreach (DataRow dr in dt.Rows)
            {
                txt_FirstName.Text = dr["firstName"].ToString();
                txt_fatherName.Text = dr["middleName"].ToString();
                txt_Surname.Text = dr["surname"].ToString();
                txt_ReportDisplayName.Text = dr["reportDisplayName"].ToString();
                txt_address.Text = dr["address"].ToString();
                txt_CnicNo.Text = dr["cnic"].ToString();
                txt_HomePhone.Text = dr["homephoneNumber"].ToString();
                txt_MobilePhone.Text = dr["mobilephonenumber"].ToString();
                txt_Email.Text = dr["emailaddress"].ToString();
                txt_AcademicQualification.Text = dr["academicqualification"].ToString();
                txt_ReligiousQualification.Text = dr["religiousqualification"].ToString();
                txt_MaritalStatus.Text = dr["maritalstatus"].ToString();
                Rbtn_MedicalInsuranceYes.Checked = Convert.ToBoolean(dr["ismedicalinsurance"]);
                drp_BloodGroup.Text = dr["bloodgroup"].ToString();
                txt_LastTimeBloodDonated.Text = dr["lasttimeblooddonated"].ToString();
                txt_Occupation.Text = dr["occupation"].ToString();
                txt_FirmName.Text = dr["firmname"].ToString();
                txt_WorkAddress.Text = dr["workaddress"].ToString();
                txt_Designation.Text = dr["designation"].ToString();
                drp_Group.Text = dr["groupName"].ToString();
                txt_DateOfBirth.Text = dr["dateofbirth"].ToString();
                txt_DateOfJoining.Text = dr["dateofjoining"].ToString();
                //  drp_CurrentPosition.Text = Convert.ToBoolean(dr["volunteerpositionid"].ToString());
                txt_PrevInsitutionName.Text = dr["previnstitutionname"].ToString();
                txt_PrevInsitutionJoiningDate.Text = dr["previnstitutionjoiningdate"].ToString();
                txt_PrevInsitutionLeavingDate.Text = dr["previnstitutionleavingdate"].ToString();
                
                Rbtn_FireYes.Checked = Convert.ToBoolean(dr["isfirefighting"]);

                Rbtn_FirstAidYes.Checked = Convert.ToBoolean(dr["isfirstaid"]);

                Rbtn_EnglishYes.Checked = Convert.ToBoolean(dr["isenglishlanguage"]);

                Rbtn_BombYes.Checked = Convert.ToBoolean(dr["isbombdisposal"]);

                Rbtn_CertYes.Checked = Convert.ToBoolean(dr["iscert"]);

                Rbtn_SecurityYes.Checked = Convert.ToBoolean(dr["issecurity"]);

                Rbtn_VolunteerYes.Checked = Convert.ToBoolean(dr["isResign"]);

                txt_DateOfLeaving.Text = dr["dateofleaving"].ToString();
                byte[] imgs = (byte[])dr["profilephoto"];
                MemoryStream ms = new MemoryStream(imgs);
                pictureBox1.Image = Image.FromStream(ms);

            }
        }

Here Is Stor Proc 

ALTER PROCEDURE [dbo].[UIPKGCONFIGURATION_spGetVolunteerList]
AS
BEGIN
	SET NOCOUNT ON;
	
	select -1 as volunteerid, 'Select volunteer' as volunteername, '1' as dbfullname
	union
	select volunteerid, displayfullname as volunteername, dbfullname
	from tblvolunteer
	order by dbfullname;

END

i will try drp_volunteer.SelectedValue any show me data But not working

Select volunteer value - 1 any value select get data