I got one of these too! I'm much less worried now seeing that someone else got one despite having done that stuff months ago.
I've been unable to log into IRCC account today (looks like they're having trouble with the website again according to their twitter, not that they ever aren't lol) and I can't get through to an agent on the phone either. I'm guessing a lot of people got these and that's why nobody can get ahold of them?
Are you going to resubmit your receipt through the web form when the website is up and running again, or just leave it? I didn't get a copy of my medical exam because it was sent electronically a few days after I completed it.
Oh no! I did it a few weeks ago and hopefully no physical mail is in transit. I don't have much hope though lol. I'll let the new tenant know that important mail might come for me and cross my fingers.