Otech — trying to drag money from me

My cousin registered at otech company website on march 15 2019. They had mentioned that he need to complete 10000 captcha in10 days. He tried to complete the task but from day1 the site is showing as error. Today he received a call from an unknown person and he is demanding 9.5k as penalty and if he don’t pay the money he said that he is going to take legal action. Please help me out to get clear this issue.