You can be reinstated though, generally, the PC 1000 statute says you only get one chance. If the public defender's office doesn't return your calls, go into their office personally and request help. If that doesn't work, you can go in and put yourself on calendar. That would likely lead to the public defender in that court room getting handed your case and warranting that he or she speak to you.
If you can't get reinstated on PC 1000, there is a good chance you are eligible for Prop. 36, which is another program similar to PC 1000 wherein you complete a drug program and get your case dismissed.