They keep calling and hanging up. What are they up to?

Calls several times a week.  When I answer, there is no response.

When I finally answered this call, it was the "Alabama Sherrif's Association" begging for a "donation".  They have been calling me 2-4 times a day for months!

Really annoying - they call ALL THE TIME - we don't answer, but they never leave a message

OK FIRST. TELL THEM YOU MAY LIKE TO DONATE AT A LATER DATE. ASK FOR THEIR ADDRESS TO THE FACILITY. THEN EITHER GOOGLE EARTH THE LOCATION AND CALL THE NUMBER IT GIVES FOR THAT ADDRESS DEMANDING TO PRESS CHARGES AGAINST THE OWNER OF THAT ( PO-BOX OR MAILING ADDRESS ) FACILITY. I MYSELF MAY DRIVE 1+ HOURS TO FIND THIS PLACE TO DEMAND THE OWNERS OR LAW ENFORCES HAVE A CHAT WITH MY ATTORNEY. MAYBE SOME LAWSUITS WILL STOP THEM FROM HARRASSING PEOPLE. CALLING DAILY AFTER BEING TOLD NOT TO IS A CRIME (HARRASSMENT). SOME PEOPLE DON'T HAVE FREE LONG DISTANCE AND COSTS TO EVEN ANSWER IT. SO YES EVERY REVOLT AGAINST THAT NUMBER AND POST THE LOCATION / MAILING ADDRESS IF ANYONE GETS IT PLEASE !
                                         P.S EVEN THOUGH THEIR THE LAW
                                             DOESN'T MEAN THEY CAN ASSUME
                                             TO BREAK THE LAW.