I'm glad to assist you with that matter.
The User Centre + app on iOS and Android is linked directly to your Customer Centre on Vidéotron's website.
If you don't have the Customer Centre login created yet, please go ahead and create one from that page. All the info needed are on your Vidéotron's bill (such as your account number).
That username and password will then work on the mobile version (User Centre + app) and allow you to see and change a lot of things in your Vidéotron's account, right at your fingertips.
Here is a support link to see what the Customer Centre is capable of (on mobile and tablet) and on your computer. http://support.videotron.com/residential/customer-centre/how-log-in-customer-centre/user-centre-plus