If certain people can't call you, they should report it to their carrier (Shaw). If Shaw disputs that the issue is in Shaw, get them to make a call to the line from a cell phone while they are talking to Shaw help about this.
It is one of the worst types of situations to resolve, but you're not likely to get anywhere by calling Telus about it...
Shaw's back end team should be looking into it as well as it's still quite likely on their end if only two SHAW customers are unable to call you. Shaw just doesn't like putting the effort into these issues.