Can you put the phone to factory reset and then install the SIM card and then restart the phone? This worked for me but don't do it if you have data on your phone that you haven't put on the cloud first.
Starting to think a lot of these devices are trade-in devices from Telus customers and that's why a lot of them have various issues, previous owners can really mess with a device before they do a device trade-in and those techs usually give it a once over before selling it on or recycling it, usually, don't inspect them enough sadly, so you wind up with locked phones or other issues not found, they'll see it looks in fine condition cosmetically and that it powers on but won't test further usually.
Oh dear well that's a whole different issue. You will need to contact customer support and find out why you were sold a locked phone. Hopefully they can can contact Apple to get it unlocked as it should have never been sold to you in that condition.
Do you have another phone you can use in the meantime?
Edit:
To submit a ticket click on SIMon at the bottom of your screen. If he gives you the runaround you can also send a private message by clicking below....
It's very likely that your iPhone is still locked to your old carrier since your model was released in September 2017 a few months before the new WCC regulations came into effect requiring all devices to be sold unlocked.
Contact your old carrier with your IMEI# of your phone and ask them to contact Apple to unlock your device. They are required to do so upon request, free of charge and without delay. Once Apple unlocks your iPhone you will need to connect to wifi or iTunes for any software updates and follow the instructions to update your carrier profile to public mobile so that your mobile data will work.
