Sadly Tina, you don't understand who you are donating to. They may call as the Kidney Foundation and hopefully this is their legal full name see National Kidney Foundation, Inc. 30 E 33rd St NEW YORK NY 10016 Phone (442)888-1300 https://www.sos.wa.gov/charities/search_detail.aspx?charity_id=8866 using charity fundraisers Donor Care Center Inc. https://www.sos.wa.gov/charities/search_detail_cfr.aspx?cfr_id=24607 and Automotive Recovery Services, Inc. https://www.sos.wa.gov/charities/search_detail_cfr.aspx?cfr_id=29123 who only give a portion of your donation to the charity.
I did try the North Carolina's Charity search database https://www.sosnc.gov/search/profcorp/9123724 that showed the National Kidney Foundation Inc as registered but with documents from 2009. Good work there NC with your consumer protection!
This is a legitimate caller. The National Kidney Foundation calls to ask if you have items to donate, and to schedule a pickup. They only come if you have items. They will call you again the night before scheduled pickup to remind you to put the items out for them.