A lot of times you will answer to a hang up dial tone associated with this number. On the rare occasion you get a live person, simply tell them you are a Federal Law Enforcement Agent ordering them to remove your number from their list immediately or you will take steps to find out who they are and have their details forwarded to the IRS for 'special treatment'. End of problem.
I continue to receive messages from this # throughout the year, they never leave a message, and call late into the evening (2044hrs). They claim to be the "Cancer Fund of America". Never heard of that charity, so hang up.