My father died without a will. I hired a lawyer to help me with probate. It has been over 2 months & he does not return my calls. How do I fire him?

My father died without a will. I hired an attorney 2 months ago and he cashed my retainer check. He got the tax id for the estate account. However, he has not done anything further. I have called repeatedly and there is always an excuse why he can't come to the phone. He finally picked up after 2 weeks and apologized saying that he was busy but he would work on my case and call me by the end of that day (which he did not). Later that week on Friday, I called again but refused to hang up until he came on the line. He said he would call me that Monday to set up a time to go to the courthouse to get a surrogate certificate. He never called. How do I go about letting him go? The retainer letter said that I agree to pay him half of the retainer now & the other half once the surrogate certificate makes the accounts available. I'm not sure I will get my retainer back. Also, since he hasn't been honest, I'm concerned that he will try to bill for work that he obviously didn't do.