County of Riverside Department of Child Support Services DPSS Riverside Child Support Failed to File Judgment with Court after 20 years $200k plus in Arrears dismissed Riverside California

I opened a case with the Riverside County Department of child Support Services in 1993. A supplemental case was filed in 1998 and a judgement filed with the court on that date.  After 20 years of child support being owed and collected sporadically with a current balance due of over $200k the county has now informed me that they FAILED to properly file the first judgement with the court and therefore both judgements are  now void.  They have also informed me that I can now be sued by my ex-husband for any money he has previously paid as there was never an official judgement in place.  

He has avoided paying past due support by quitting jobs, moving, and or working under the table for the past twenty years.  What has been collected through wage garnishment he can now sue for.  Not to mention that he was even put in jail for 30 days for willful failure to pay child support.  He can now also sue for wrongful imprisonment.  The county now tells me there is nothing they can do.  I am out any unpaid support owed and I can be sued by him for any amount that was taken from him.  My case worker even admitted that they dropped the ball.  

I don't even know where to start to find an attorney to take a case against the county.  Can any please help me? The county now wants to close my case because there is a $0 balance owed.  I keep saying this can't be happening! How does he get away with hiding and not paying support and now he gets to walk away free and clear of any debt after owing over $200,000+ in past due support.  If anyone knows an attorney who might take this case please forward the information to me.