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If you want to cancel your service, you need to set up a call back through Koodo assist.

Then talk to a agent.

Did you turn off roaming on your phone? Have you tried to set your device to select your network manually? That way, your phone will not be connecting to a roaming tower and you will not incur any additional fees. It should also be noted that you should not post any personal details, as this is a public forum. 

Wether you are with Koodo or someone else, whenever you are near a border, the phone will connect to the best network. If USA is the best network, then that’s the phone’s fault and not Koodo. Make sure you do as MilyWay suggested.

Note that if you restart your phone the network settings go back to automatic and you need to set it as manual to Koodo again.