You hit the right answer the second time, just make up a date. I do that with all those annoying check inquired. Random phone number, random zip, random birthday. The questions are silly, but getting all indignant about it takes time, random answers get me on my with my product which is what I want, and gives them crap info for the demographics.
Whenever I am paying cash and asked for zip code, I use 96919 which is Guam. Let the marketers figure that out.
For my phone number, I used to use local police dept number.