Toll free number problem outside of USA

Ourr clients outside of USA unable to reach us via our toll free numbers (we have two).

Following page shows that "When you have a toll-free number from Comcast, your customers can reach you from anywhere in the U.S., Canada, Guam, the U.S. Virgin Islands and Puerto Rico."

http://businesshelp.comcast.com/help-and-support/voice/phone-get-a-toll-free-number/

I just confirmed with a client in Canada, not working.

Please help.