As far as I learned, nobody has received AOR (file number) since mid July 2019 up to now. You may contact CIC via web-form just to make sure they have received your application.
There is no confirmation email. You will receive a response shortly (2-3 businesses days). Please keep us posted. I am in the same situation, waiting for AOR for about 6 months.
I think this is simply an answer to your follow up email. I also received a similar response when I followed up my application through web form. I do not know why they do not send AOR (including file number)!
Actually, the time between the date of issues was 12 days (based on the letters). It is better to call them. If your interview letter is issued they will tell you the date (I mean the interview date).