WWW and php issues

I'm getting "The type WWW' does not contain a constructor that takes 2' arguments" my code is :

 using UnityEngine;
 using System.Collections;
 
 public class WWW : MonoBehaviour {
     public string url = "http://..website../unity.php?";
     public string Username;
     public string Password;
     public bool canLogin;
     private WWW getdata;
     
     void Start () {
     
     }
 
     void Update () {
 
     }
 
     void OnGUI(){
         Username = GUI.TextField(new Rect(10,10,200,20),Username,25);
         Password = GUI.PasswordField(new Rect(10,10,200,20),Password,"*"[0],25);
     }
 
     IEnumerator www(){
         WWWForm form = new WWWForm();
         form.AddField("Username",Username);
         form.AddField("Password",Password);
 
         getdata = new WWW(url, form);
         yield return getdata;
 
     }
 }

it's unfinished but it's almost done anyways, its saying 'getdata = new WWW(url, form);' is the issue, but every thing iv'e looked at says that's okay, i also can use getdata.text, only .guitext, so anyone know where i messed up? it's probably obvious to someone, first time trying to access data from my site.