How to avoid duplicated records when concurrent requests make within a second in Laravel

please help me to find out the issue.

Sometimes (not always) my following code inserts two records in DB (into user table as well as profile table ),but i am checking before inserting that the "mobile_no" is already exist or not that to make unique mobile number based records.

 static function postData($data) { 

    try {
if (isset($data['number'])) {
    //exist
    $exist = Profile::where('mobile_no', '=', $data['number'])->get(); 
   //print_r($exist);

    if (count($exist) > 0 ) {       
    $user = User::find($exist[0]['user_id']);
    if (isset($data['last_name'])) {
    $user->first_name = $data['first_name'];
    }
    if (isset($data['last_name'])) {
    $user->last_name = $data['last_name'];
    }
     if (isset($data['email'])) {
    $user->email = $data['email'];
    }
    $user->save();
    $proid = $exist[0]['user_id'];
    $profile_result = Profile::find($proid);


    if (isset($data['number'])) {
    $profile_result->mobile_no = $data['number'];
    }
     if (isset($data['birthday'])) {
    $profile_result->dob = $data['birthday'];
    }



    $profile_result->save();
    return $exist[0]['user_id'];
    }else{

    $user = new User();
    if (isset($data['first_name'])) {
    $user->first_name = $data['first_name'];
    }
    if (isset($data['last_name'])) {
    $user->last_name = $data['last_name'];
    }


    $user->save();
    $id = $user->id;
    $profile = new Profile();

    $profile->user_id = $id;

    if (isset($data['mobile_number'])) {
    $profile->mobile_no = $data['number'];
    }
    if (isset($data['birthday'])) {
    $profile->dob = $data['birthday'];
    }
    $profile->save();

    $proid = $profile->user_id;
    $profile_result = $profile::where('user_id', '=', $proid)->get();

    $user_result = $user::where('id', '=', $id)->get();

    $output = array();




    return (string) $id;
    }
    }

    } catch (Exception $ex) 
    {
    return $ex;
    }


    }

via azeem