You would need a subpoena to gain access to the number directly, which may be more trouble than it is worth. However, although a drastic change, you could change your mobile telephone number at no charge by reaching out to customer service.
Prior to caller id, nobody knew who was calling them before answering the phone. After the fact, people still have the ability to conceal their identity prior to the call being answered. If you don't wish to be bothered by un-identified calls, there's an option on your phone to ignore the call, although you could be missing something important.