What can I do if someone is blackmailing me with my private photos and

I become friend with someone on dating app that person send pics of another guy and took my private videos with my face now he is blackmailing me as I met him, I got to know that he is different man. he is blackmailing me to go for make out with him then he will delete my nudes. What to do? He is calling me again and again, he knows my area where i am living. Even he said up to 31st December he gave me time to go for sex with him. But I said no to him. Still he is calling and blackmailing somehow.