Harassment from an Author

I have been receiving a large amount of harassing unwanted e-mail from an author who claims that he is a professional writer. Today I sent him one email that requests he stop emailing me or I will report him to his ISP provider. What kind of person harasses someone to this extent? He must have a lot of time on his hands. This author’s harassing emails include the link to his book publisher. I have emailed his book publisher to make them aware that he may just be violating their toss agreement.