To keep my telephone number and to avoid losing minutes, I too buy one year of service on my Tracfone before leaving the US (actually buy four 60 minute “cards” so with double minutes on the phone I also get lots of minutes along with the one year of service).
I now use a credit card issued by a US based bank along with a US address so I can buy minutes on-line or on the phone itself. But before this, I WAS able to buy minutes on-line using my CDN credit card IF I didn’t log onto Tracfone’s web site FIRST. Going on-line to Tracfone’s web site, I selected the “buy minutes on-line option” without logging in. Then when it came time to pay, I was able to select Canada as the country which allowed me to then enter my CDN address. This wouldn’t work when I logged into my Tracfone account before attempting to buy minutes. I don’t know if one can still get around the US address thing in this manner.
I tried once to add minutes on-line when I was still in Canada and had no service to the Tracfone. I was able to add the minutes on-line using the credit card/address work-around noted above but, of course, since I had no service to the phone these added minutes did not show up on the phone itself. The next time I crossed the border and had phone service, the minutes did show up on the phone, but only after going on-line to Tracfone’s web site and retrieving a string of numbers to punch into the phone. In this case, the extra minutes were added before my time on the phone actually expired so I don’t know if just updating the minutes on the web site alone would have kept the phone active or not. Maybe someone has experience with that.