Hi Chariklo, you did well !
My response to the "it's the truth" crap will be in future "Does Truth change ?" , then I will point out if I get the chance, that what I taught as truth from the late fifties to the late noughties changed in a major way at least once a decade, if not more, how can they be sure what they say is "Truth" now will not change again ?
The religion I grew up in teaches nothing today as it did then. (Some doctrines have only been modified rather than dropped, but that statement still stands)
For you, if they call again , I would follow up with another letter and say the only contact you will consider is by letter, anything else, even a publication through the door, you will consider harassment and will take legal action. ( You don't have to agree to a letter, but I had fun with one Elder for a few exchanges, till I hit him with the prove the 1919 choosing by Jesus thing, and strangely , three years later, I am waiting for his reply !)
The letter to the COBOE/BOE worked for me. I got a nice letter back saying if I ever needed any help, or just to talk, call the Bro, he even added his cell phone number as well as his landline.
No one has called since, I have seen them knock all around me, even on what I know is a DNC opposite, but not on me.