Can you double check that the people calling you have the right number and are dialing 1 then your number? There is no + or 00 or whatever needed as Canada and the US share the same country code and numbering plan.
I talk to my sister almost daily, and she appeared to be not answering, so I facebooked her, she was answering but I'm not getting them. We ran several tests, no answer. I have checked that everything is correct with my phone as has she.