I'm afraid you did nothing to even slightly slow them down, :(. Call centers have telecom equipment that we don't that allows them to put any damn number onto your caller id than they want. Given the complaints I see here and in other places, I'd bet they're calling from a call center. And it could be anywhere. If you want to actually cost them real money, you can do two things: You can just set the phone down and let their recording blather on and on--thereby tying up one of their telco trunks--or you can do what my 82yo mom does (and she knows what she's doing): let the recording play, and when she eventually gets a real human, she doesn't yell at them or anything, but rather she engages in prattling chitchat with them. Every single moment she has them on the phone, she's costing them money. And she knows it. And I'll tell you, she actually likes it.