I haven't received my tax return yet, and it is already September. Whom should I contact for this? I am currently not in Canada and cannot find a contact number/email.

If you are not in Canada you can contact CRA directly by placing a collect call to CRA at 613-940-8495.   To place a collect call you will dial zero to contact the operator and advise them that you want to make a collect call and give them the number you are trying to reach. This way you will be able to place this call and charges will be reversed.