you can state plainly and clearly

"MRs so and so DOESNT live here. you have the wrong number. I am asking you to NOT call here anymore. I cannot help you, and if you continue to call this number, I am going to call the police and report the harrassment." ask them to repeat to you that they have the wrong phone number.

if they call back, tell them you found a phone number for them. Give them the local number of the local police department. not 911, but the standard regular number for your local PD. That should make it plain that you are not playing.

I hate these people.