I use a software called phonetray - not it is not free, but it works...I simply block the number and add a voice reply like "Not accepting calls" or "Not accepting Telemarking calls" among several options.  When this number come in, it rings once and that it!  I can block up to 1,000 numbers, and accept the same number by adding them to a white list and have the option of adding a name or some other note to let me know who is calling...it displays on the PC screen, announces the caller name and number...nice.....