That's kinda correct. They are responsible for the wiring up to and including the box that is attached to your home. This is called the "point of demarcation" or "demarc" for short. This is the box the article advises you to lock up. Unless you can prove (via video or similar) that someone attached to your cable beyond the demarc, they will assume that the calls originated within your house wiring and therefore is your responsibility.
They MIGHT come to some agreement, especially in this case where it is happening to several businesses/churches/residences around town. But they are will first assume you are trying to be a weasel.
The easy thing is to block everything you don't intend to use.
And most Telcos charge anywhere from 1 to 5 USD per month to block 900 calls.
Better to dump the land line altogether if you are worried about this. Port you r home number over to the cell and away you go.