Credit card svcs like all the other calls mentioned. I use the app Blacklist. Once I get one of these calls, I put their number on that list. No more calls from that number. I never answer a number I don't recognize. I might google the number to check it out. If your phone doesn't have blocking features, just use an app.
Received a call on 3/9/15 at 6:55 p.m. on my cell phone (don't know how they got that number, because I only use my landline for business calls). It was one of those scams to 'lower my credit card debt'. I waited on the line purposely to tell them I was reporting their information to the FCC. LOL of course they hung up on me.