Caller ID said "Alarm Co". They keep changing their number. This week, I got the same Caller ID on:
206-307-0053, 469-470-0980, 704-207-0883, and 805-639-8729. I blocked all of them.

"Alarm Co" has been calling for weeks at 7:14 am!  I have answered them twice and told them to take me off their list -- but they keep calling.  I have blocked them but my stupid phone still rings once -- why?  I thought the point was to block the number -- period.

My phone rings once too.  My info booklet that came with the phone says it has to ring once to know that is the number you want blocked.

I answered this call the first time to find out what they wanted.  It is a home security system that they want to charge a monthly fee for.  I informed the caller that I am on the Do Not Call List.  They were ignorant as to what that was.  I have since put a block on the number but they continue to call every day.  Today, so far, they have called twice.  My phone rings once to verify that is the number I want blocked so I know it is the same caller.