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What phone are you using? Some will ignore the setting to download certain updates.
If you are suggesting you are being billed for data you have not used, the only test for that is to turn your phone off entirely, and allow for differences in time zone between your location, and where the billing is calculated (not always where you are).
I checked my account and I see a few instances of unexpected data usage (highlighted) but none of any significance. It's possible my WiFi dropped briefly during those times. There is never any usage overnight when I have my phone on and plugged in the charger.
NFtoBC asked you what model of phone you are using but you didn't reply. It's possible your phone is set to aggressively switch to mobile data if it detects weak/unresponsive WiFi. I know I loose WiFi in certain parts of my office so switching to data at the office is not unexpected for me.
This might seem like a silly suggestion, but have you tried removing your SIM for your device overnight to see if any data is logged on your Telus account? If you give that a try and data usage still appears on your account for your SIM when it isn't even in the device. My guess is your SIM card might have been cloned somehow. It might be wise to ask Telus to void and replace the SIM.