Hi Maggie65,
First thing the IRCC will contact you is thru your email address that you had provided. If you put your email address at your citizenship application form? From there, you'll received a AOR notice from IRCC indicating that they had received your application like most of us here. On that email, includes your Application number starts at C000 and your UCI # still the same. If you didn't include your email address then you'll get your AOR thru mail.
By the way I received my AOR just a few days ago. I'm using my UCI # for checking my eCAS but you can also used the application # whatever that suits you. Try also to check your email inbox and spam maybe IRCC sent your AOR already. Goodluck to all of us...