Thanks for your first post and welcome to our forums page.
Very sorry to hear you are having issues with this. We don't have a way of barring any incoming calls to your landline so is this a function you have available on your landline handset/ If it is, could this have been set up accidentally?
Also, are the people calling you from Canada able to call other UK numbers? If they haven't tried this, please can you get them to give this a go as this would narrow down whether this could potentially be an issue with their number.