I called the number back and it said if I want to be on the do not call list press 9, I did, then it said it will take 72 hours to be added to their do not call list. crossing fingers
I would advise against calling unknown numbers back. Doing so often lets bogus companies know that your phone number is legitimate and they will likely end up calling more frequently. The best "free" solution is to have your number registered on the National Do Not Call list and to never answer calls from numbers which you don't recognize. It will take time, but the number of scam calls you get will eventually go down.