Nevada is a 2 party state so you will have to inform him that the call is being recorded. When he calls and asks for you, tell him "Please hold while I turn my tape recorder on". If he objects then hang up. When they send you their dunning letter, respond with a DV and at the bottom in large bold print put
"ALL CALLS TO MY HOME ARE RECORDED"
If they call after signing for your DV, record away.