1) Do not answer callers you aren't familiar with.
2) You should also consider a call blocking device or even a phone that offers this option. There are number are a number of models out there. Do your research and find the one that fits your needs.
3) Most importantly. Report the calls to both the FTC and the FCC.
What good is reporting the calls to the FTC? They want a company name and address - deliver the data to them on a silver platter, so they can take that very last step. They also are among the "bigger government" departments that have had their operating budgets slashed by Congress. I don't know how many fraud investigators they may actually have, but I think we all know that it is FAR less than needed.
I know about call blocking and I have a very good one on my cellphone. It has over 230 different numbers in it currently! These scammers are PERSISTENT, I will give them that.