Who called from 3127595255

Person on other end claims to work for the CDC doing a random survey. The survey is about kids and cell phones.
I just told them I didn't have kids, and they ended the survey.

we also got a few missed calls from that same phone number 312-759-5255

I got two calls from this number within the past few days; no voicemail was left either time.

My phone number is unlisted, so how am I getting a call from someone I don't know? This is the second call in 3 days.

i keep getting this call, i don't answer, and no message left.......