This sort of questioning is their only really strong tool against someone doing NOTHING, like not going to meetings but not being seen to critisise the WTS (or otherwise sin) either. It's best dodged, but that's hard to do.
When that question was asked, I knew I was on a hiding to nothing and took a risky approach to kill it off....
I said that I'd been doing some soul searching and looked up heritic and apostate in the dictionary.
I said that from this I realised that if I said Yes, then I'd be a dictionary-definition heritic because I wasn't acting in accord with my beliefs; and if I said No, then I'd be a dictionary-definition apostate for turning against my beliefs....
I said that I was sure I wasn't either of those things, although I wasn't sure how I felt right now - partly becuase I was having a tough mental and emotional time right then...
They looked at me like I was mad (which was good, as that was part of my fast tactical withdrawl under covering fire strategy - ill health is about the only acceptable excuse for eccentric behaviour for the JW's), accused me a few times of using smokescreens to avoid talking about it all and to dodge the question, but couldn't find a scripture that said that was a sin, so they left and didn't bother me much more after that....
Not too long later I moved a long, long, long way away...
My advice - DO NOT try this dangerous tactic at home!!
Max