Caller ID shows only "San Francisco, CA", so I let it go to voice mail but they left no msg.  It's close to another number (only last 2 digits changed) that has been calling me and others on here, so I suspect it is one of many consecutive numbers these telemarketers use.  I am just adding them to my blocked list.

Same thing just happened to me. I didn't answer and no message was left.

The caller is trying to rip you off. He is very rude!! He is selling dental insurance for 40.00 a month. He was running a special for 200.00 every 6 months. I ask him to send out information so I could read more about the plan because I have the 159.00 plan with Aethna, the very same plan he is trying to sell for a lot more. He told me the cheaper rate only covers cleaning and has limits. That is a complete and total lie!!!
If you only want the discount plan for one you can buy that online for 100.00 and the family plan is 159.00 a year not 480.00.
This is like spam you get in your email. Who do you report spam by phone?

Same thing. I let it go to voice...TG for caller ID! I know my numbers are on the National DO NOT CALL list, so what is going on???

The Do Not call list is less then worthless. It  relies on your DA to prosecute offendors and they generally have no interest in doing anything of the kind.

However, you can report them to the FCC, https://esupport.fcc.gov/ccmsforms/form1088.action

Be sure to fill out the form completely.
Also- I like to keep a log of their calls, so when theycall again and you file another report you can list all the previous calls and times.