i added the $40 international add-on before going to Europe 2 weeks ago. However, I had no signal at all in the middle of Barcelona or London even though my wife's work phone was fully operational. Frankly disappointed that I wasted $40 and had no usable phone.
While travelling outside the US, there are 2 reasons why your phone might not work.
Have you added the free international roaming package from self serve? If you didn't add it, that might explain why your phone didn't work. You could always try calling Koodo and maybe they will credit you the amount you paid.