overwhelming amount of telemarketing calls that I'm unable to block from getting through to my line.

I get calls from a certain area code several times. I block the number and report it as spam, however, eventually I receive more calls from same area code only the other 7 digits are different. No matter how many times I block and report the numbers, they continue to get through by changing the last 4 or last 7 digits RELENTLESSLY. How can I stop them???