Here is your comeback:
You feel STUMBLED. That's exactly the word you want to use: STUMBLED.
That is a trigger word for JWs - it means that in your eyes, they have brought reproach on their religion (by treating you with contempt) and that is not how they want to be perceived by outsiders.
The other phrase you want to use is along the lines of how you had always heard that JWs were so LOVING, but the way your are being treated doesn't feel LOVING to you. This brings up the conflict of how they ought to treat you and puts it opposite to how they actually are treating you. Again, it comes down to their behaviour having brought reproach on the belief system, and that is not how they want to be perceived.
I would put it out there and focus on those two concepts and be righteously indignant about it. I would expect that the invitation will be forthcoming, and then I would promptly RSVP that I will NOT be attending. Just to make it YOUR choice, not theirs.