My cousin activated his sim card on December 1st (billing date), as well as the add-ons calls and texts.
As of December 12th, he's left with 20 days for texts and 51 days for calls. So only calls are until the end of the month + 1 month.
For the add-on calls, it's more advantageous to always activated the add-ons on the 1st day of your cycle to get the most of the 60 days.
"In other words, if there are 10 days left on your current payment cycle, your Add-On will be valid for approximately 40 days."
As for the add-on texts, it's unclear to me whether you are only left with 10 days if you activate the add-on on the 20th day of your cycle (which would be totally offensive and barbaric) OR you actually get 30 days from the day you activate it (the most logical option).
To play it safe, always activate on the 1st day of cycle.
@Pat D. If that's the case, if could very well be a bug.
From this page (https://fizz.ca/en/faq/what-is-an-add-on-and-how-do-i-buy-one), we understand that ALL add-ons are on the same terms. There shouldn't be an exception whatsoever. Otherwise it's false advertisement.
Let's try to get support to confirm.