In my case, I live in Calgary, but I thought the same thing as you. I didn't want to go back just a few days before Christmas and stay away from my family during the holidays.
I sent the email to
IRCC.DN-CITIZENSHIP-CEREMONIES-RN-CITOYENNETE-CEREMONIES.IRCC@cic.gc.ca and filled out the Web Form with the same message. I'm not sure which one is the best. In theory, emailing them should be enough as that is what they point out as a communication channel in the invitation PDF.
If you sent them an email already, probably they've already updated your file as well. I know it's frustrating when you don't know what's happening and need to guess.
In the worst-case scenario, if you really want to call them, you can try Skype. I've already called them before via Skype. You need to add some credits there though, but the price per minute is super cheap, like a few cents.