...don't want? A company constantly calls me trying to sell me male erection pills. I tell them I don't need them and to stop calling, but they continue to constantly call me.
When the phone rings, just pick it up and say nothing. Set it down and let them talk to the air. I do it all the time with telemarketers. They don't make money on wasted time. I try to waste as much of their time as I can. Hell, I'm retired, I've got the time to waste. When you talk to them, you are giving them a potential channel for them to change your mind. Say nothing.
I've also acted like a hard of hearing person - keep asking them to repeat themselves. Frustrates the hell out of them. When they say erection pill, you could say "I've paid my electric bill." or "Electric eel? I don't have an electric eel."
Your call might be a robo-call. Just press a number to speak with someone, then try to waste their time.
Tom Mabe (check some Youtube videos) has fun with telemarketers.