But writing to them will cost you a stamp.
I used an online form to tell them to stop bothering me. They still imply that they will send out a detector van to check up on me.
They might find that difficult as I am more than 1/4 mile from any public road.

I don't use Facebook as I mistrust the security of it and so it will be letters or phone calls or emails in order to contact them as far as I am concerned.