I had a long conversation with one rather bright young man that wanted me to not cancel. I cited chapter and verse of their editorializing in their news section (I made it clear to the lad that they had every right to say whatever they wanted to on the OP-ED page) and he was...speechless.
I used to do the same, then found out that the caller is not an employee of the paper. The caller works for a marketing firm.
Then I learned another trick, but it depends on how the caller starts the pitch. If they ask "has the delivery been timely?" I say "Yes!" If they ask whether or not I enjoy the paper, or similar, I tell them I am delighted. End of call, everybody's happy, and I am the only one the wiser.