Agree with everyone above that we should all NOT answer a phone call if we don't know the number.
If necessary, change your phone number to get some peace from the a*&%$loes. And definitely report them to the Consumer Financial Protection Bureau, your state attorney general, and the Better Business Bureau.
Changing your phone number could leave you open to even more calls for the previous owner of that number. Almost all phone numbers are recycled and most people keep their number. The major reason they get rid of it is scam calls.