Why did you feel ashamed of yourself? If you hadn't done it you may have felt disappointed in yourself at a missed opportunity.
It does take courage and all the emotions may cause us to behave in a way that is not ideal but you know better for next time if tha is the way you feel.
What you did was great. Here are two JWs going from house to house, generally unwelcome and trying to recruit people into their cult, to get trapped like them. Given their age, it is likely that they shun someone related to them. They are happy to lecture everyone else, they won't accept any non JW religious leaflets, what's left? Openly telling them what's wrong with their religion. Well done.