Scammers! This (fake) "organization" has been calling off  and on for 15 years. The phone numbers they use appear to be spoofed or burner phones so it's a waste of time to research where you think the call is coming from (based on the number appearing on your call display). They change number extremely frequently so blocking their number doesn't last long - they just continue calling using different numbers. They never leave messages but if you do talk to them they do sound intimidating, and they pressure you hard for "donations" (which probably is quite effective when they're talking to seniors).