to stop a judgement/ they claim its my girlfriends

a collection agency started garnishing my wages, and they claim its my ex girlfriends account. last year they attempted to garnish but my employer did not grant it because the social did not match. Then I think my employer released my info, and they used what is called skip tracing. someone told me that you can get anybodys info with just the name. now how can I stop that bogus judgement, and sue for my stress and
time. I had no idea the judgement existed because they were serving it to a p.o. box to continue it. I requested copies from my employer. And is there someone that can help me on a local level? I live in visalia california my phone:559 300 9663