Additional charge on my bill

Be careful what you wish for. If Easy Roam was triggered, it means you connected to cellular networks outside Canada. Without Easy Roam, your bill would be much higher.

That's the issue.  You don't have to sign up for it.  As soon as your device connects to a tower on a roaming partners network where your plan doesn't have included service for.  EasyRoam kicks in automatically.  If you don't want this to happen in the future.  You can request that Customer Care put an international block on your service or put your device in Airplane Mode before leaving the country and leave it in Airplane Mode the whole time while traveling.  WiFi can be turned on while a device is still in Airplane Mode.  

Any billing charges you will have to contact Telus to address the issue. You can reach out to them here. I recommend twitter for the best response time.