This FAQ link should answer your questions:
https://www.koodomobile.com/en/help/explaining-koodos-3g-usage-price-increase

Hi there,

So that is for a few reasons. If you're using an old 3G capable device that cannot use LTE you're charged the fee as 3G is being phased out. This also goes if youre using a newer device that uses 3G for calling and does not have VoLTE turned on.

So that's pretty much it, if you have an old device then you need to upgrade to remove the fee to an LTE and VoLTE compatible device. That, or if you have a compatible device, turn on the VoLTE feature and then the fee will be removed after 30 days. I hope this clears things up! More information can be found in the link

https://www.koodomobile.com/en/help/explaining-koodos-3g-usage-price-increase

Edit: seems like Allan got to it

But I am on a 5G device? I am using an iPhone 15? 

When did you switch to the iPhone 15?, and a couple of other questions: 1. is anyone else on the account with an older device? 2. under your cellular settings, is the VoLTE feature turned on?

Do you have the VoLTE add-on in your self serve under your Plans>Add-ons

Hi ​@jlhmcq, you’ve been using the iPhone 15 since early September and as it is a VoLTE eligible device, the $3 3G add-on should have dropped automatically within 30 days. We’ve now removed the add-on and added a $9+tax credit for the period it was on while you were using an eligible device. 

Thank you very much! :)