Android - No such table SQLite

I'm trying to read data from a SQLite, when I try to create the cursor to see if exists, the LogCat says :

 Process: palindrome.com.practicabasedadesxmlthreads, PID: 5229
android.database.sqlite.SQLiteException: no such table: Clients (code 1): , while compiling: Select * from Clients where NIF LIKE '55554454P'
        at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
        at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:889)
        at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:500)
        at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
        at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
        at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
        at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)
        at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1314)
        at android.database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1253)
        at joancolmenero.com.practicabasedadesxmlthreads.MainActivity.NumeroDNI(MainActivity.java:81)
        at joancolmenero.com.practicabasedadesxmlthreads.MainActivity$1.onClick(MainActivity.java:41)
        at android.view.View.performClick(View.java:4456)
        at android.view.View$PerformClick.run(View.java:18462)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5102)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
        at dalvik.system.NativeStart.main(Native Method)

I created a Toast to see if db is null when the APP starts, and it says it is not. I did it with :

Conexion = new ClientsSQL(MainActivity.this, "Clients", null, 1);
    db = Conexion.getReadableDatabase();
    if (db == null) {
        Toast.makeText(MainActivity.this, "I'm NULL",
                Toast.LENGTH_LONG).show();
    }
    else{
        Toast.makeText(MainActivity.this, "I'm not NULL",
                Toast.LENGTH_LONG).show();
    }

This is my cursor, I tried also without dniCreat, and still giving me the error:

Cursor c;
        c = db.rawQuery("Select NIF from Clients where NIF LIKE '"+dniCreat+"'", null);
        coincideix = !c.moveToFirst();
        c.close();

And finally this is my SQLiteOpenHelper, where I create the Sqlite :

public class ClientsSQL extends SQLiteOpenHelper {
    // Declaramos la sentencia para crear la tabla
    String sqlCreate = "CREATE TABLE Clients(NIF String, cognom1 String, cognom2 String, nom String)";

    public ClientsSQL(Context context, String name, SQLiteDatabase.CursorFactory factory,
                          int version) {
        super(context, name, factory, version);
        // TODO Auto-generated constructor stub
    }
    @Override
    public void onCreate(SQLiteDatabase db) {

        db.execSQL(sqlCreate);
        db.execSQL("INSERT INTO Clients VALUES ('39410028B', 'hola1', 'Hola2', 'Jonathan')");
        Log.v("INFO1", "creating db");


    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub
        // Si existe la tabla, la borramos y la volvemos a crear.
       db.execSQL("DROP TABLE IF EXISTS Clients");
        db.execSQL(sqlCreate);
    }

}