Why can't I send SMS messages from my iMessage app on my computer when I used to be able to do so?

I actually seem to recall it was about the time that Shaw, my Internet provider (WiFi) was transitioning to new owner, Rogers. But when I spoke with them about my problem they said they couldn't help me with my Apple iMessage issue! I talked at length with Apple and all my settings are set properly and they couldn't help me. Apple's published support information says that receiving and sending SMS messages on my computer's iMessage app is possible. I had been able to do this until suddenly I couldn't send anymore. Telus support, where I get my cellular coverage, also said they can't find a reason for my problem either. I wonder if other Apple iMessage users on their computers are now experiencing the same issue since Rogers took over from Shaw, if they are their Internet provider?