relation does not exist in postgreSQL but already exist

I've read a lot of articles about my problem but no one solve it. So u can see my code here

DATABASE_URL = os.environ.get('url_of_my_db')
con = None
try:
    con = psycopg2.connect(DATABASE_URL)
    cur = con.cursor()
    
    print('PostgreSQL database version:')
    #cur.execute('SELECT version()')
    #cur.execute('SELECT * FROM qwerty')
    
    #cur.execute(sql.SQL('SELECT * FROM {}').format(sql.Identifier('qwerty')))
    #cur.execute(sql.SQL("INSERT INTO {} (chat_id, username, created_on) VALUES (8985972942, vovakirdan, 2022-01-05)").format(sql.Identifier('users')))
    cur.execute("""INSERT INTO users (chat_id, username, created_on)
                    VALUES (3131,
                    vovakirdan,
                    2022-01-05)""")
    

    # display the PostgreSQL database server version
    db_version = cur.fetchone()
    print(db_version)
       
     # close the communication with the HerokuPostgres
    cur.close()
except Exception as error:
    print('Cause: {}'.format(error))

finally:
    # close the communication with the database server by calling the close()
    if con is not None:
        con.close()
        print('Database connection closed.')

and in my DB table named "users" (named without quotes) are exist, but I still have this error: error

...relation "users" does not exist

all the #commented code doesn't work and send the same error besides SELECT version(), it works perfectly that proves that connection works.

The problem was that PostgreDB wants me to use SELECT colum FROM schema.table instead of SELECT colum FROM table. And that's all. Thanks everyone