One issue you likely have is the SIM not being active. Usually if a SIM is not used for about 45 days, it is deactivated and can no longer be used. A replacement would be needed. It's best to contact Telus directly to inquire.
The app itself won't care if there is a SIM card in the phone or not. I can use it on wifi with my old phone just fine and it doesn't have a SIM installed.
As for billing issues or trouble accessing your account, you'll need to contact Telus directly. No one on the forum here will have access to your account as most of us are just Telus customers.
Maybe the App doesn't detect the SIMCARD and won't let me have access to the account without detecting the SIMCARD usually linked to it or something.
You can try logging in using a browser on any device.
How did you get the message about an outstanding balance? Have you verified that message is legit and not a scam?
How were you getting your monthly statements previously? If you had an outstanding balance you should have received a statement indicating the balance.