I would have responded by saying that I have heard the Good News of Jesus Christ, and that the Bible is my foundation for all things pertaining to faith and practice. God's Word needs no "addition" to it. You could keep a stack of Gospel tracts near your door so you can give it to them. I don't know if they would read it, but who knows?

As for sitting down with them and having a lengthy discussion, I don't know. On one hand, we are to preach the Gospel in season and out of season, but, on the other hand, cults are the hardest nonbelievers to deal with.

True godliness is a sincere feeling which loves God as Father as much as it fears and reverences Him as Lord, embraces His righteousness, and dreads offending Him worse than death~ Calvin