Filed ch.13 bankruptcy for an amount of child support arrears that differed from the amount the LA County Court Trustee's office but they did NOT contest your amount in court. Was their amount void?

Your question is nonsense from the git-gat.

You CANNOT get relief from child support in bankruptcy. There is nothing for them to reduction in what you owe is allowed. Out of the courts jurisdiction.

I feel so sorry for your kids, getting stuck with a parent that is obviously bankrupt in more ways than financial.