JW's get to have the upper hand in how much or how little they will shun their family members and you are supposed to be grateful for whatever crumbs they throw you. You've taken the wind out of their sails by turning the tables on them. I've thought about saying to JW's I run into from time to time... " I hate to sound harsh but are you still a JW? If so I can't in good conscience speak to you if you are still part of that misleading and destructive organization."
The difficult part of this lies in the fact that they are your parents and they are quite elderly. It's hard to be forgiving even when you know that they too are victims of a cult.