I received such a call too today and it showed private number and I could not take the call and later the number showed. When I called back the number did not even ring once.
Strange ?????
NEVER press any prompts to remove as this just VERIFY'S they reached someone with a valid number and they will hound you to death until you change your phone number. This also applies to email's, never click to remove your email address as this also verify's a valid address and you will only get more and more spam if you do. best thing to do is block the numbers using your carrier's applications and also block using spam controls in your email. Don't let these scum bags get the best of you !