Jane,
Please post your list of 27 numbers you have blocked. You have more than I have.
Hello, I recently got one, only one so far, I am lucky. One suggestion to make them stop is to place the phone not in service tones at the beginning of your answering machine message. The pause for 3 seconds and then give your message. The tones will tell the robo-dialer that this is not a working number and delete it. It may take a few weeks for this to work through all the different spammers who are calling.
Here is the link describing the details:
http://wolfram.org/writing/howto/phone.html
Here is the actual tone link:
http://sbaratz.home.mindspring.com/MISC/telezapper_SIT.wav