Document each time you call (or look at your phone records to see when you called). Hopefully, you didn't just wait until the last minute to start caring about your case. But if you really have been trying to get in touch with them and you don't feel prepared, don't go forward with your trial. Be sure to tell the Judge that you do not feel the attorney is prepared, that you haven't met with them, that you don't know what the trial strategy is and you haven't even discussed it, tell them the dates and times of your calls, etc. Ask the judge for a continuance (and perhaps another attorney, but that might not happen).
If it is a public defender's office, ask for their supervisor and complain to them.
Legal disclaimer: Brian Tevis is licensed to practice law in the State of Georgia. All information given is based only on Georgia law and is not directly applicable to any other jurisdictions, states, or districts. This response, or any response, is not legal advice. This response, or any response, does not create an attorney/client relationship. The response is in the form of legal education and is intended to provide general information. Any state-specific concerns should be directed to an attorney who is licensed to practice law in that respective state.