Getting Charged for local calls on an unlimited calling plan

I have heard of a practice similar to what you are describing ages ago on a US carrier forum, just missing one important detail. It sounds like Telus is picking up on the device of the person you are calling potentially being out of the country, even though it goes to their voicemail. So that would mean your call is being forwarded to a device that is roaming and then being bounced back to voicemail if they don't answer and registering as a billable call when it should not be.

Hopefully Customer Care can sort this out for you. If not, reach out to the Executive Office, leave a message, and someone should get back to you within a week at the longest.