Not to mention that I already applied for Citizenship in December 2019 and my application is still under process.
I'm hoping that on your newer urgent application you mentioned that you sent one in September so as to avoid any confusion. As a future reference, I'm not 100% about this but I'm quite sure that you can let the IRCC know that you'd like to make an application you've mailed in already, don't know the procedure though.
In any case, your application has started processing and should be complete in a few days if everything is good. In regards to your September application, you'd probably receive an AoR for it right about this week or the coming one, but given you've gotten an AoR for the urgent one, it's hard to say what'll happen now.
The citizenship application pre-COVID takes
at least a year, so you can be assured that it's probably being processed but expect it to take a WAY longer time since you sent it just before the pandemic.