Ok, so this may be an expensive and time consuming option, but it's an idea nonetheless.
The inability of the FOC to collect probably has to do with jurisdiction and the lack of a compact between Michigan and Alabama. So here's a way you can put this into Alabama jurisdiction.
1) Get a civil judgment, in Michigan, against your ex for all the past due, plus 8% interest per year, plus your attorney's fees and court costs. You'll need a lawyer for this, but Michigan law allows for the recovery of attorney fees in civil cases.
2) Next, you'll need to find a lawyer in Alabama and have the judgment "domesticated," which means that a court in the State of Alabama enters it as a judgment in Alabama. The Alabama court is, theoretically at least, constitutionally required to do this ("full faith and credit" clause).
3) Now that you have a civil judgment in Alabama, follow the procedures for collecting on the judgment (i.e. garnishment).
There may be an easier way. A family lawyer should be able to figure it out for you. You can't really depend on the FOC or the AG to help you.
Best of luck!