Called but did not leave msg.

Keeps calling our business, sometimes multiple times a day. Mostly no one is on the line or they refuse to say who they are with.

Called them back and they have a recording saying that they partner with various firms for fundraising efforts.  You can leave your number if you don't want to be called but they also want you to list the company for which you would like to opt out.  However, they do not give you the specific names of their partners so that is not really possible.  I just blocked their number on my phone.