Calls every hour, from 9am till 6pm... Never leaves message, calls 7 days a week... Who is this?

Calls all day and you can't call the number back. Can anyone please find out who this is?

EVERYDAY, MANY MANY times a day. Relentless. Rings 3 times, never even activates answering machine (takes 4 rings for that). Even when we answer, no one responds on other end. Assume it is a bot call, but is ridiculously annoying, especially when my husband is home, sick and trying to sleep off his chemotherapy side effects. DNC registry is a total, ineffective joke, so doesn't matter that we've been on it for a long time.

They JUST called back trying to sell us roofing services. Didn't catch the company name, though.

(720) 862-3991 -  NBI OF COLORADO.
I attempted to call this number.  100% fake.
Adding to my Ooma black list immediately.