I feel like you have to be outright rude sometimes with people who don't get the point. I can see how this might be hard but it's actually a great skill to have because some people out there just don't get the hint/or are downright assholes.
"Thanks, we'll call you if we feel the need to talk to you" and literally walk away (my elders came hounding to the door). Or hang up the phone. It really is easy once you give up that need to be nice.
I actually have long discussions with my children about the need to be rude (firm/assertive) sometimes, especially my daughter - sounds counter-intuitive as a parent but it's really not.