No message was left but I called back to find they're a fundraising company that calls on behalf of charities & political organizations. They offered an automated feature to get on their do not call list and I did that plus I blocked the number.
This # belongs to MDS Communications, a telephone fundraising company who call on behalf of non-profits and political entities. They claim they are exempt from the federal do not call list, but will keep their own do not call list which you can sign up for by phone or on line.
It was Non-profit " Heifer International/Heifer.org" I too was frustrated by the constant hang ups. So I called the number back and learned that it is an organization I VERY MUCH support! I voiced my concern that they are likely losing countless donations because So Many of us screen calls. If they'd take a moment to say who they are or if caller ID showed Heifer.org, many would answer, call back and donate.