If you want to block calls like this I suggest you check out Google Voice. You contribute, by marking these calls as "spam" to a blacklist that google analyzes and pushes through on future spam filter updates.
Also when you block a number, a message is broadcast to the caller "Beeep Beeeep Beeeeeeep The number you have dialed is no longer in service. Please check the number you are dialling and try your call again."
How great is that??
Plus you can enable a call record option that plays a quick audible recording that discloses that the conversation is being recorded. But it plays so quick, its only purpose is for plausible deniability.
And you can screen the person's message live as they leave it.
And set a schedule of when to ring which phone on what schedule.
It's a virtual number (and yes they port numbers in so if you want to keep your number ... ) that has multiple numbers (i.e. office, home landline, mobile, etc.) so you never have to change your number again. You just keep plugging whatever number you want into your Google Voice dashboard and wallah!!