When my iPhone updates it turns airplane mode off and I get charged for roaming

Use Airplane Mode on your iPhone, iPad, iPod touch, and Apple Watch - Apple Support

Airplane mode turns off the wireless features on your device so that you comply with airline regulations.

About cellular data roaming options for your iPhone and iPad - Apple Support

Turn off Data Roaming or prepare for a trip

Need to avoid roaming charges because you arrived at your destination without an international data plan? Turn off Cellular Data and Data Roaming.1,2 Open Settings and tap Cellular, or Cellular Data, or Mobile Data. Turn off Cellular Data, then tap Cellular Data Options and turn off Data Roaming.

Also turn off Wi-Fi Assist......About Wi-Fi Assist - Apple Support

With Wi-Fi Assist, you can stay connected to the Internet even if you have a poor Wi-Fi connection. For example, if you're using Safari with a poor Wi-Fi connection and a webpage doesn't load, Wi-Fi Assist will activate and automatically switch to cellular so that the webpage continues to load. You can use Wi-Fi Assist with most apps like Safari, Apple Music, Mail, Maps, and more. 

If your device was truly in Airplane mode, it would not have Wi-Fi and therefore could not "update" itself, unless you're enabling Airplane mode and then turning Wi-Fi on. Is that what you're doing? If so, are you doing this from Settings or from Control Center? If from Control Center, try doing this only from Settings to see if there's any difference.

From Control Center, I know that disabling Wi-Fi and Bluetooth is only temporary, but Airplane mode from Control Center should not be temporary (but perhaps there's a bug?)

you are missing something...take the time to read the links !

okay good is that helping ? airplane mode does not have to be on, if still an issue I would suggest you contact Rogers or Apple Support

Click "Contact Support" top right corner of this page