I *almost* had to sue my neighbours about the fence. What a fiasco it was.
Basically go to the town small claims court. They have attendants there to help you. To file costs $100. You'll need the name and address of the person you are suing. If you don't have this (although it sounds like you do), you can go to Service Ontario and pay $10 to find out who owns the property.
You can retain a lawyer if you want, but you don't have to with small claims, although it helps because those fools at the office don't know WTF they are talking about. When I asked about my fence issue they told me they don't deal with my issue (meanwhile a lawyer waiting with his client said they do and gave me advice, and the town office also told me it was a civil issue).
Small claims I think forwards the information to the person you are suing (I think!)
Just make sure you take a photo with the DATE IMPRINT. Seriously. Enough judge judy has shown me that you need this.
Also demonstrate that you've tried to make contact (times, dates). You want the judge to easy find in your favour. If they don't show you win, but that doesn't necessarily solve your problem.
ETA: i would say that you should send a registered letter first, indicating your "threats"-- but if time is of the essence, this might not be ideal.
