An app is definitely needed. Your website is also slow to load. The UI on a mobile device is not very good and would be much better on an app, along with notifications etc. Telus has one, as so many other mobile company sites. PM should catch up.
I very much doubt that a mobile app would with with the self serve website being slow. In the past, some of these cell phone carrier account apps have been almost nothing more than a bookmark to a mobile version of the website, except in a standalone app.