I had success by porting my landline to Google Voice Account, which has global spam filtering.
First, get an AT&T GoPhone ($20). Then port to Google Voice ($20), choosing AT&T as the option.
You are asked for a transfer id that you will need to call AT&T for... It is NOT on the phone, and not available without calling AT&T's support #.
I don't know your story, but this also makes you more flexible to either drop your current landline, or move to a cheaper provider (likely).
Either way, Google Voice does wonders at spam filtering, but some still make it through. Best of luck!