Depending on the County there should be a Circuit Defender who can be appointed to do post conviction relief. His claim that that office was the cause of his Habeas may cause a conflict of interest, I suggest you contact an attorney who specializes in post conviction relief see if you can get a consultation and fully explain your situation with all possible paperwork you may have.
It does not sound like your son's habeas petition has been granted yet, only that he filed one. The next step will be for a judge to hold a hearing on the petition. If it is granted then his case basically starts over. I am not aware of public defenders being provided for habeas cases in most counties and your son really needs a lawyer to represent him in this kind of proceeding.