I'm not in Canada, but we did have to take this step.
In our case, the MOW was constantly contacting my FWH. When we blocked her phone, she simply got another one.
The lawyer prepared a letter stating she had to stop any and all contact. He referred to the law she'd be breaking and enclosed a copy of it. It was hand delivered by a process server so she couldn't claim she didn't get it.
Since I'm not familiar with your judicial system, I don't know if there's a similar statute that your OW would be in violation of.
It cost $300. Well worth the 4 months of peace we've had since.