You should appear in court and work out any differences you have with your attorney. You risk having your bail revoked if you fail to appear or be ready to go forward with your matter.
If the court refused to release the lawyer then you are stuck with him unless you can convince the court to release him. A certified letter won't do it.
I am licensed in Pennsylvania. Members of my firm are licensed in various states, including Pennsylvania, New Jersey and New York. We handle cases involving personal injury (car accidents slip and falls, etc.,) medical malpractice, nursing home abuse, workers' compensation and social security disability. This post is not legal advice, but instead contains general educational information. Please do not act or refrain from acting based upon what you read in this post. Also please remember that this post does not form an attorney/client relationship between you and me. If you have specific legal questions, you should contact an attorney in your state for assistance.
I agree with my colleagues. I often am curious when individuals "fire their attorneys" whether it is done because the attorneys are failing them or because they are being told things that they wish not to hear. You may need to work with them so I suggest you evaluate that. If they have failed to interview witnesses, return phone calls, answer questions, then you need to communicate this to the court. Be specific with who they have not spoken to. Have specifics ready. These are true issues. The court may be more concerned that you are purposely delaying the proceedings.
This is not intended as individual legal advice and there is no attorney client relationship established by this answer. It is advisable that you seek individualized legal assistance. This is not a substitute for hiring an attorney.