It's entirely possible the app is not yet compatible with Nougat. I have the exact same error with it on my S7 and S6 Edge. I'd say wait until they release an update.
For now, try accessing your account online instead.
In regards to the My Telus Account App, I had an issue over the weekend. Everytime I tried to log in I got an error message "unable logging you in. Please try again later". I connected to the chat feature, spoke to Katherine who was absolutely the best at trying to help me fix this issue. She coached me through the steps to provide the information she required. This morning I tried to log in with my email address and password. IT WORKED!!! RIGHT ON!!! Now whenever I am away from my computer I can access my account. Thank You once again Katherine!!! MOST APPRECIATED!!!