Unable to block this number

Someone called today at 12:05 PM and my answering machine picked up.  My answering machine picked up and they did not leave a message.  The caller ID said "Name Unavailable".   I'm betting it is a scammer!

WIll not take "not interested" for an answer. Rude!

These people keep calling me about a survey. I was nice at first and told them I don't do surveys and to please take my number off. Now I'm not nice. Doesn't matter to them. English is definitely not their first language. It says this number is from the US, but that can't be. I called this number and the recorded message is that the number is not valid. They had just called me. It has to be an overseas number with numbers missing. I'm getting several of these a day. Today, have already had two from same number. They interrupt whatever I'm doing. It's got to be a phishing expedition. Don't tell them anything.

Number comes up name not found.  when answered  a foreign voice said something I could not understand. When I      said what? they hung up