Use this script when the phone rings:
Caller: Hello, can I speak to you?
You: That's me.
Caller: Do you want to buy some crap I'm selling?
You: No, thank you. [I'm not interested in that.]
Caller: But what if I sweeten the deal with more crap for the same price?
You: Again, no thanks. But thanks for calling. I have to go now. Bye.