After your boyfriend's ex-girlfriend broke up with him, she extorted money from him, which constituted extortion. You can report the case to the public security organ and ask him to be investigated for criminal responsibility. The law is based on Article 274 of the Criminal Law of People's Republic of China (PRC): whoever extorts public or private property in a large amount shall be sentenced to fixed-term imprisonment of not more than three years, criminal detention or control; If the amount is huge or there are other serious circumstances, he shall be sentenced to fixed-term imprisonment of not less than three years but not more than ten years.
Her behavior has constituted a crime of extortion. You can keep her phone records.