Alert them of your situation so that they can intervene as appropriate. Also some state anti-stalking laws allow you to convict the stalker just based on the initial phone calls, letters, and visits. Reserve calling 911 for situations in which you think you are in immediate danger. They may have more time for you than a patrol officer, and may be more familiar with stalking issues. If you communicate with one officer regularly, that officer is more likely to recognize a pattern of conduct.
Telephone companies have divisions and personnel who specifically deal with harassing phone calls.
Unfortunately, you may not be able to rely upon the police or the courts to keep you posted on your case. Inquire about the status of your case, and insist that the police take appropriate investigative or enforcement measures. Apply for a restraining order, but do not expect that a protective order will necessarily deter a stalker. Be aware that in some instances, restraining orders can prompt a more violent reaction from the offender. But applying for a restraining order is an important step in building a file against the stalker.