If you're not interested in reducing spam calls to your mobile number, just go back to Facebook. If you're using an iPhone, just go back to Facebook.
Now that we've got the crowd thinned out, go to the Google Play Store and download the latest Phone app.
Open the Phone app and tap the hamburger menu in the top right corner.
Tap on "Caller ID and spam".
Then slide "Filter spam calls" to the right.
Lifehacker has an article here.