Telus Won't Stop Billing Me for Cancelled Account

I had a cell phone service with Telus. I cancelled it and they disconnected my cell phone but they continue to bill me every month. I am out of the country but the only way to phone them is through a 1800 number which doesn't work internationally.

Their website only allows you to submit emails if you have a valid account (but mine is cancelled now). So basically I have no way to stop them billing me every month short of cancelling my Visa card.