Sorry to hear that Gary, I can't really offer any advice as I have never been in that situation. However would you be able to contact a local MP? (Member of parliament, I'm not sure of the local politics where you live) and say that you feel you're being harrassed?
Though obviously you have nothing to worry about, they live in clean conditions, are well fed and well looked after. I think they'll give up after a while after one or two visits, even if they do that many.
Although it may be official that they have to visit you, they may not and it could just be going through the motions and mandatory regulations to inform you of visits. Fingers crossed