Answer call and set up an appointment when you know when you won't be home. Waste their time. If they call back set up another appointment when you know you won't be home again.
This number has called us nine times in nine days that I have been keeping records. I started keeping track on Dec 8 and they have called 9 x since then. I have told them several times not to call any more, one time I told them I was keeping a record of their calls and had reported them to the National Do Not Call registry (not that they are doing anything about it.) the last few calls today they haven't said anything at all. Just call and say nothing. I am taking this another step higher and complaining to the local Sheriff Dept, for aggravated harassment.