how to check in my dabase if the value is existing?

Question

im using asp.net mvc 5 im new bee here. my problem is i have a tbl_register the content is 

 

Username

password

repeat-password

contact number

 

then i fill up the form, all i need is to validate if the contact number is existing to another table in tbl_client. this is my code. my code is not working

 

var agent = _clientService.Find(x => x.ContactPrimary == newUser.ContactNumber);

                  if (agent != null)
                  {
                      var client = new Client
                      {
                          ParentClientId = agent.FirstOrDefault().Id,
                          FirstName = "",
                          LastName = "",
                          MiddleName = "",
                          Suffix = "",
                          ContactPrimary = "",
                          ContactSecondary = "",
                          Age = 0,
                          Gender = "",
                          CountryId = 0,
                          StateId = 0,
                          CityId = 0,
                          TownId = 0,
                          EmailAddress = "",
                          Postcode = 0,
                          Commission = 0,
                          SubAgentCommissionPercentage = 0,
                          Address = ""
                      };
                      _clientService.Add(client);
                  }