The Studiokuma filter has worked pretty well for me. Wish I'd had it earlier.
It's quite funny, I was on Studiokuma (it's now called Call Defender) and it's works really well. Almost too well.
I want to extend my contract with Smartone (they offered double the speed for same $88/m) - now they want to call back, but it seems they have no number that is not on the block list. Almost hillarious.