Support Arrears: How Can I Stop Interest on Unpaid Child Support

My question involves child support in the State of: Texas and Arizona

Here are some facts, My husband had a daughter born in Texas, a while after the divorce the ex moved to Arizona without his knowledge, then there in Arizona she filed for child support. He had an order of $36,000 which he has gotten down to approximately $12,000, of that $4,000 is principle and $8,000 is interest.

Now some more facts: His daughter committed suicide 12 years ago at the age of 17 in Arizona and she is buried under a different name than what was legally on her birth certificate. The mother somehow changed her middle and last name even had her enrolled in school under this other name. The mother has not been on public assistance and has a substantial income.

My husband was paying everything accordingly until he lost his job and even then he was recieving unemployment where they continued to take out the same amount for child support as if he was still making the same amount of money. Then the unemployment was appealed and they won so the last payment for support was recieved in December 2012. And his IRS refund was taken, however it does not show as a payment just yet. My husband has now recieved three letters stating that they will suspend his license. We've already been to the Office of the Attorney General to say we will voluntary send payment in.

My question is this, if we could possibly come up with the principle amount how can we get rid of the arrears? Which brings up another question, how much of a payment, if any, goes to the principle?

I read in another post that if she would agree then we could, but we do not even know where she is in Arizona. Plus there is a lot of blaming going on.